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 $191.68   12.632%   $215.893   $215.89   $215.90   $215.90  
  Purchase #2 $69.53   9.381%   $76.0526   $76.05   $76.05   $76.10  
  Purchase #3 $46.80   7.229%   $50.1832   $50.18   $50.20   $50.20  
  Purchase #4 $54.47   13.134%   $61.6241   $61.62   $61.60   $61.60  
  Purchase #5 $160.71   9.428%   $175.8617   $175.86   $175.85   $175.90  
  Purchase #6 $181.76   7.162%   $194.7777   $194.78   $194.80   $194.80  
  Purchase #7 $168.45   7.248%   $180.6593   $180.66   $180.65   $180.70  
  7 purchase totals = $873.40       $955.0516   $955.04   $955.05   $955.20