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 $92.83   12.544%   $104.4746   $104.47   $104.45   $104.50  
  Purchase #2 $66.95   13.565%   $76.0318   $76.03   $76.05   $76.00  
  Purchase #3 $202.82   3.678%   $210.2797   $210.28   $210.30   $210.30  
  Purchase #4 $25.78   5.734%   $27.2582   $27.26   $27.25   $27.30  
  Purchase #5 $129.63   4.551%   $135.5295   $135.53   $135.55   $135.50  
  Purchase #6 $146.57   6.797%   $156.5324   $156.53   $156.55   $156.50  
  Purchase #7 $154.68   6.237%   $164.3274   $164.33   $164.35   $164.30  
  7 purchase totals = $819.26       $874.4336   $874.43   $874.50   $874.40