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 $59.42   11.356%   $66.1677   $66.17   $66.15   $66.20  
  Purchase #2 $234.87   9.541%   $257.2789   $257.28   $257.30   $257.30  
  Purchase #3 $16.31   7.391%   $17.5155   $17.52   $17.50   $17.50  
  Purchase #4 $136.35   8.507%   $147.9493   $147.95   $147.95   $147.90  
  Purchase #5 $148.76   13.431%   $168.74   $168.74   $168.75   $168.70  
  Purchase #6 $230.90   8.118%   $249.6445   $249.64   $249.65   $249.60  
  Purchase #7 $57.43   7.480%   $61.7258   $61.73   $61.75   $61.70  
  7 purchase totals = $884.04       $969.0217   $969.03   $969.05   $968.90