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 $101.35   9.637%   $111.1171   $111.12   $111.10   $111.10  
  Purchase #2 $42.56   10.395%   $46.9841   $46.98   $47.00   $47.00  
  Purchase #3 $74.52   10.541%   $82.3752   $82.38   $82.40   $82.40  
  Purchase #4 $161.90   9.556%   $177.3712   $177.37   $177.35   $177.40  
  Purchase #5 $69.96   7.501%   $75.2077   $75.21   $75.20   $75.20  
  Purchase #6 $105.82   9.804%   $116.1946   $116.19   $116.20   $116.20  
  Purchase #7 $32.36   10.352%   $35.7099   $35.71   $35.70   $35.70  
  7 purchase totals = $588.47       $644.9598   $644.96   $644.95   $645.00