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 $47.81   12.253%   $53.6682   $53.67   $53.65   $53.70  
  Purchase #2 $207.86   10.643%   $229.9825   $229.98   $230.00   $230.00  
  Purchase #3 $236.33   3.863%   $245.4594   $245.46   $245.45   $245.50  
  Purchase #4 $131.33   11.859%   $146.9044   $146.90   $146.90   $146.90  
  Purchase #5 $234.94   8.777%   $255.5607   $255.56   $255.55   $255.60  
  Purchase #6 $5.43   10.669%   $6.0093   $6.01   $6.00   $6.00  
  Purchase #7 $115.58   7.715%   $124.497   $124.50   $124.50   $124.50  
  7 purchase totals = $979.28       $1,062.0815   $1,062.08   $1,062.05   $1,062.20