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 $33.46   8.233%   $36.2148   $36.21   $36.20   $36.20  
  Purchase #2 $245.53   4.798%   $257.3105   $257.31   $257.30   $257.30  
  Purchase #3 $222.67   3.249%   $229.9045   $229.90   $229.90   $229.90  
  Purchase #4 $89.67   9.182%   $97.9035   $97.90   $97.90   $97.90  
  Purchase #5 $14.71   11.485%   $16.3994   $16.40   $16.40   $16.40  
  Purchase #6 $221.46   3.113%   $228.354   $228.35   $228.35   $228.40  
  Purchase #7 $86.90   12.383%   $97.6608   $97.66   $97.65   $97.70  
  7 purchase totals = $914.40       $963.7475   $963.73   $963.70   $963.80