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 $175.58   11.657%   $196.0474   $196.05   $196.05   $196.00  
  Purchase #2 $240.43   9.539%   $263.3646   $263.36   $263.35   $263.40  
  Purchase #3 $135.72   3.604%   $140.6113   $140.61   $140.60   $140.60  
  Purchase #4 $19.76   5.479%   $20.8427   $20.84   $20.85   $20.80  
  Purchase #5 $178.71   12.872%   $201.7136   $201.71   $201.70   $201.70  
  Purchase #6 $156.79   8.211%   $169.664   $169.66   $169.65   $169.70  
  Purchase #7 $25.65   12.594%   $28.8804   $28.88   $28.90   $28.90  
  7 purchase totals = $932.64       $1,021.1240   $1,021.11   $1,021.10   $1,021.10