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 $161.49   11.834%   $180.6007   $180.60   $180.60   $180.60  
  Purchase #2 $32.90   7.378%   $35.3274   $35.33   $35.35   $35.30  
  Purchase #3 $94.46   4.200%   $98.4273   $98.43   $98.45   $98.40  
  Purchase #4 $70.68   8.285%   $76.5358   $76.54   $76.55   $76.50  
  Purchase #5 $5.31   12.420%   $5.9695   $5.97   $5.95   $6.00  
  Purchase #6 $68.56   9.405%   $75.0081   $75.01   $75.00   $75.00  
  Purchase #7 $123.31   9.554%   $135.091   $135.09   $135.10   $135.10  
  7 purchase totals = $556.71       $606.9598   $606.97   $607.00   $606.90