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 $111.32   13.331%   $126.1601   $126.16   $126.15   $126.20  
  Purchase #2 $111.39   9.620%   $122.1057   $122.11   $122.10   $122.10  
  Purchase #3 $187.90   5.317%   $197.8906   $197.89   $197.90   $197.90  
  Purchase #4 $6.85   9.105%   $7.4737   $7.47   $7.45   $7.50  
  Purchase #5 $29.91   7.818%   $32.2484   $32.25   $32.25   $32.20  
  Purchase #6 $16.52   3.109%   $17.0336   $17.03   $17.05   $17.00  
  Purchase #7 $227.91   9.754%   $250.1403   $250.14   $250.15   $250.10  
  7 purchase totals = $691.80       $753.0524   $753.05   $753.05   $753.00