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 $62.46   4.334%   $65.167   $65.17   $65.15   $65.20  
  Purchase #2 $94.61   10.138%   $104.2016   $104.20   $104.20   $104.20  
  Purchase #3 $116.63   8.385%   $126.4094   $126.41   $126.40   $126.40  
  Purchase #4 $79.27   8.753%   $86.2085   $86.21   $86.20   $86.20  
  Purchase #5 $125.53   10.731%   $139.0006   $139.00   $139.00   $139.00  
  Purchase #6 $211.39   10.377%   $233.3259   $233.33   $233.35   $233.30  
  Purchase #7 $73.27   4.766%   $76.762   $76.76   $76.75   $76.80  
  7 purchase totals = $763.16       $831.0750   $831.08   $831.05   $831.10