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 $229.93   11.238%   $255.7695   $255.77   $255.75   $255.80  
  Purchase #2 $172.69   7.504%   $185.6487   $185.65   $185.65   $185.60  
  Purchase #3 $156.75   13.227%   $177.4833   $177.48   $177.50   $177.50  
  Purchase #4 $28.63   12.744%   $32.2786   $32.28   $32.30   $32.30  
  Purchase #5 $73.29   3.664%   $75.9753   $75.98   $76.00   $76.00  
  Purchase #6 $25.78   3.130%   $26.5869   $26.59   $26.60   $26.60  
  Purchase #7 $207.74   5.485%   $219.1345   $219.13   $219.15   $219.10  
  7 purchase totals = $894.81       $972.8768   $972.88   $972.95   $972.90