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 $72.52   5.317%   $76.3759   $76.38   $76.40   $76.40  
  Purchase #2 $199.41   7.134%   $213.6359   $213.64   $213.65   $213.60  
  Purchase #3 $122.65   5.386%   $129.2559   $129.26   $129.25   $129.30  
  Purchase #4 $77.51   6.229%   $82.3381   $82.34   $82.35   $82.30  
  Purchase #5 $25.75   10.805%   $28.5323   $28.53   $28.55   $28.50  
  Purchase #6 $77.63   13.413%   $88.0425   $88.04   $88.05   $88.00  
  Purchase #7 $235.91   10.700%   $261.1524   $261.15   $261.15   $261.20  
  7 purchase totals = $811.38       $879.3330   $879.34   $879.40   $879.30