Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $42.32   13.163%   $47.8906   $47.89   $47.90   $47.90  
  Purchase #2 $177.27   8.283%   $191.9533   $191.95   $191.95   $192.00  
  Purchase #3 $201.26   11.836%   $225.0811   $225.08   $225.10   $225.10  
  Purchase #4 $233.41   4.343%   $243.547   $243.55   $243.55   $243.50  
  Purchase #5 $112.63   5.205%   $118.4924   $118.49   $118.50   $118.50  
  Purchase #6 $249.60   8.127%   $269.885   $269.89   $269.90   $269.90  
  Purchase #7 $34.80   9.186%   $37.9967   $38.00   $38.00   $38.00  
  7 purchase totals = $1,051.29       $1,134.8461   $1,134.85   $1,134.90   $1,134.90