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 $245.39   8.654%   $266.6261   $266.63   $266.65   $266.60  
  Purchase #2 $53.39   9.636%   $58.5347   $58.53   $58.55   $58.50  
  Purchase #3 $158.76   3.863%   $164.8929   $164.89   $164.90   $164.90  
  Purchase #4 $244.64   4.457%   $255.5436   $255.54   $255.55   $255.50  
  Purchase #5 $154.95   8.353%   $167.893   $167.89   $167.90   $167.90  
  Purchase #6 $21.79   8.611%   $23.6663   $23.67   $23.65   $23.70  
  Purchase #7 $5.84   11.635%   $6.5195   $6.52   $6.50   $6.50  
  7 purchase totals = $884.76       $943.6761   $943.67   $943.70   $943.60