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 $141.49   9.845%   $155.4197   $155.42   $155.40   $155.40  
  Purchase #2 $31.79   7.151%   $34.0633   $34.06   $34.05   $34.10  
  Purchase #3 $43.63   13.175%   $49.3783   $49.38   $49.40   $49.40  
  Purchase #4 $134.99   11.733%   $150.8284   $150.83   $150.85   $150.80  
  Purchase #5 $216.65   10.601%   $239.6171   $239.62   $239.60   $239.60  
  Purchase #6 $38.80   4.381%   $40.4998   $40.50   $40.50   $40.50  
  Purchase #7 $62.55   9.414%   $68.4385   $68.44   $68.45   $68.40  
  7 purchase totals = $669.90       $738.2451   $738.25   $738.25   $738.20