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 $67.63   8.161%   $73.1493   $73.15   $73.15   $73.10  
  Purchase #2 $207.60   9.272%   $226.8487   $226.85   $226.85   $226.80  
  Purchase #3 $240.29   7.149%   $257.4683   $257.47   $257.45   $257.50  
  Purchase #4 $54.92   11.780%   $61.3896   $61.39   $61.40   $61.40  
  Purchase #5 $90.96   11.567%   $101.4813   $101.48   $101.50   $101.50  
  Purchase #6 $204.71   13.344%   $232.0265   $232.03   $232.05   $232.00  
  Purchase #7 $92.31   9.830%   $101.3841   $101.38   $101.40   $101.40  
  7 purchase totals = $958.42       $1,053.7478   $1,053.75   $1,053.80   $1,053.70