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 $14.47   5.850%   $15.3165   $15.32   $15.30   $15.30  
  Purchase #2 $235.74   10.517%   $260.5328   $260.53   $260.55   $260.50  
  Purchase #3 $52.61   10.633%   $58.204   $58.20   $58.20   $58.20  
  Purchase #4 $103.30   11.448%   $115.1258   $115.13   $115.15   $115.10  
  Purchase #5 $144.77   11.494%   $161.4099   $161.41   $161.40   $161.40  
  Purchase #6 $249.30   6.154%   $264.6419   $264.64   $264.65   $264.60  
  Purchase #7 $135.95   9.350%   $148.6613   $148.66   $148.65   $148.70  
  7 purchase totals = $936.14       $1,023.8922   $1,023.89   $1,023.90   $1,023.80