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 $202.39   10.843%   $224.3351   $224.34   $224.35   $224.30  
  Purchase #2 $148.89   9.139%   $162.4971   $162.50   $162.50   $162.50  
  Purchase #3 $51.78   13.605%   $58.8247   $58.82   $58.80   $58.80  
  Purchase #4 $39.71   4.837%   $41.6308   $41.63   $41.65   $41.60  
  Purchase #5 $72.62   10.407%   $80.1776   $80.18   $80.20   $80.20  
  Purchase #6 $46.31   9.205%   $50.5728   $50.57   $50.55   $50.60  
  Purchase #7 $210.56   11.371%   $234.5028   $234.50   $234.50   $234.50  
  7 purchase totals = $772.26       $852.5409   $852.54   $852.55   $852.50