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 $213.54   10.570%   $236.1112   $236.11   $236.10   $236.10  
  Purchase #2 $217.34   12.421%   $244.3358   $244.34   $244.35   $244.30  
  Purchase #3 $45.56   5.633%   $48.1264   $48.13   $48.15   $48.10  
  Purchase #4 $97.73   6.396%   $103.9808   $103.98   $104.00   $104.00  
  Purchase #5 $53.54   13.120%   $60.5644   $60.56   $60.55   $60.60  
  Purchase #6 $104.68   12.506%   $117.7713   $117.77   $117.75   $117.80  
  Purchase #7 $134.67   7.828%   $145.212   $145.21   $145.20   $145.20  
  7 purchase totals = $867.06       $956.1019   $956.10   $956.10   $956.10