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 $49.65   12.269%   $55.7416   $55.74   $55.75   $55.70  
  Purchase #2 $126.56   9.358%   $138.4035   $138.40   $138.40   $138.40  
  Purchase #3 $119.34   8.760%   $129.7942   $129.79   $129.80   $129.80  
  Purchase #4 $50.83   3.756%   $52.7392   $52.74   $52.75   $52.70  
  Purchase #5 $229.47   7.115%   $245.7968   $245.80   $245.80   $245.80  
  Purchase #6 $17.79   9.634%   $19.5039   $19.50   $19.50   $19.50  
  Purchase #7 $123.80   5.224%   $130.2673   $130.27   $130.25   $130.30  
  7 purchase totals = $717.44       $772.2465   $772.24   $772.25   $772.20