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 $116.31   6.253%   $123.5829   $123.58   $123.60   $123.60  
  Purchase #2 $163.46   11.597%   $182.4165   $182.42   $182.40   $182.40  
  Purchase #3 $64.41   10.689%   $71.2948   $71.29   $71.30   $71.30  
  Purchase #4 $185.67   5.342%   $195.5885   $195.59   $195.60   $195.60  
  Purchase #5 $32.86   6.761%   $35.0817   $35.08   $35.10   $35.10  
  Purchase #6 $160.43   9.302%   $175.3532   $175.35   $175.35   $175.40  
  Purchase #7 $24.44   3.130%   $25.205   $25.21   $25.20   $25.20  
  7 purchase totals = $747.58       $808.5226   $808.52   $808.55   $808.60