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 $114.39   4.323%   $119.3351   $119.34   $119.35   $119.30  
  Purchase #2 $207.43   12.420%   $233.1928   $233.19   $233.20   $233.20  
  Purchase #3 $94.46   8.789%   $102.7621   $102.76   $102.75   $102.80  
  Purchase #4 $140.92   6.108%   $149.5274   $149.53   $149.55   $149.50  
  Purchase #5 $97.28   13.503%   $110.4157   $110.42   $110.40   $110.40  
  Purchase #6 $60.86   3.788%   $63.1654   $63.17   $63.15   $63.20  
  Purchase #7 $119.82   3.705%   $124.2593   $124.26   $124.25   $124.30  
  7 purchase totals = $835.16       $902.6578   $902.67   $902.65   $902.70