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 $55.64   8.298%   $60.257   $60.26   $60.25   $60.30  
  Purchase #2 $43.84   13.443%   $49.7334   $49.73   $49.75   $49.70  
  Purchase #3 $49.88   10.228%   $54.9817   $54.98   $55.00   $55.00  
  Purchase #4 $70.35   9.782%   $77.2316   $77.23   $77.25   $77.20  
  Purchase #5 $113.43   13.686%   $128.954   $128.95   $128.95   $129.00  
  Purchase #6 $206.50   3.519%   $213.7667   $213.77   $213.75   $213.80  
  Purchase #7 $9.28   13.548%   $10.5373   $10.54   $10.55   $10.50  
  7 purchase totals = $548.92       $595.4617   $595.46   $595.50   $595.50