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 $167.54   3.391%   $173.2213   $173.22   $173.20   $173.20  
  Purchase #2 $228.90   5.177%   $240.7502   $240.75   $240.75   $240.80  
  Purchase #3 $239.38   12.207%   $268.6011   $268.60   $268.60   $268.60  
  Purchase #4 $141.95   12.179%   $159.2381   $159.24   $159.25   $159.20  
  Purchase #5 $136.82   11.377%   $152.386   $152.39   $152.40   $152.40  
  Purchase #6 $89.77   5.427%   $94.6418   $94.64   $94.65   $94.60  
  Purchase #7 $155.79   4.730%   $163.1589   $163.16   $163.15   $163.20  
  7 purchase totals = $1,160.15       $1,251.9974   $1,252.00   $1,252.00   $1,252.00