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 $207.97   3.394%   $215.0285   $215.03   $215.05   $215.00  
  Purchase #2 $54.96   11.215%   $61.1238   $61.12   $61.10   $61.10  
  Purchase #3 $13.27   10.183%   $14.6213   $14.62   $14.60   $14.60  
  Purchase #4 $13.76   7.443%   $14.7842   $14.78   $14.80   $14.80  
  Purchase #5 $12.50   10.744%   $13.843   $13.84   $13.85   $13.80  
  Purchase #6 $119.90   5.226%   $126.166   $126.17   $126.15   $126.20  
  Purchase #7 $51.38   3.352%   $53.1023   $53.10   $53.10   $53.10  
  7 purchase totals = $473.74       $498.6691   $498.66   $498.65   $498.60