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 $58.98   11.680%   $65.8689   $65.87   $65.85   $65.90  
  Purchase #2 $111.42   12.711%   $125.5826   $125.58   $125.60   $125.60  
  Purchase #3 $222.46   11.168%   $247.3043   $247.30   $247.30   $247.30  
  Purchase #4 $159.51   6.441%   $169.784   $169.78   $169.80   $169.80  
  Purchase #5 $49.95   9.638%   $54.7642   $54.76   $54.75   $54.80  
  Purchase #6 $187.56   3.539%   $194.1977   $194.20   $194.20   $194.20  
  Purchase #7 $60.89   4.845%   $63.8401   $63.84   $63.85   $63.80  
  7 purchase totals = $850.77       $921.3418   $921.33   $921.35   $921.40