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 $117.30   4.804%   $122.9351   $122.94   $122.95   $122.90  
  Purchase #2 $182.28   11.164%   $202.6297   $202.63   $202.65   $202.60  
  Purchase #3 $182.67   7.739%   $196.8068   $196.81   $196.80   $196.80  
  Purchase #4 $126.68   7.801%   $136.5623   $136.56   $136.55   $136.60  
  Purchase #5 $139.65   7.339%   $149.8989   $149.90   $149.90   $149.90  
  Purchase #6 $238.94   6.769%   $255.1138   $255.11   $255.10   $255.10  
  Purchase #7 $86.78   12.547%   $97.6683   $97.67   $97.65   $97.70  
  7 purchase totals = $1,074.30       $1,161.6149   $1,161.62   $1,161.60   $1,161.60