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 $69.39   8.854%   $75.5338   $75.53   $75.55   $75.50  
  Purchase #2 $12.52   9.660%   $13.7294   $13.73   $13.75   $13.70  
  Purchase #3 $195.82   10.569%   $216.5162   $216.52   $216.50   $216.50  
  Purchase #4 $58.88   12.257%   $66.0969   $66.10   $66.10   $66.10  
  Purchase #5 $57.79   6.598%   $61.603   $61.60   $61.60   $61.60  
  Purchase #6 $150.58   3.798%   $156.299   $156.30   $156.30   $156.30  
  Purchase #7 $187.55   12.126%   $210.2923   $210.29   $210.30   $210.30  
  7 purchase totals = $732.53       $800.0706   $800.07   $800.10   $800.00