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 $151.86   4.733%   $159.0475   $159.05   $159.05   $159.00  
  Purchase #2 $236.70   12.157%   $265.4756   $265.48   $265.50   $265.50  
  Purchase #3 $249.66   11.119%   $277.4197   $277.42   $277.40   $277.40  
  Purchase #4 $95.99   5.651%   $101.4144   $101.41   $101.40   $101.40  
  Purchase #5 $48.74   6.503%   $51.9096   $51.91   $51.90   $51.90  
  Purchase #6 $229.59   3.437%   $237.481   $237.48   $237.50   $237.50  
  Purchase #7 $119.32   11.251%   $132.7447   $132.74   $132.75   $132.70  
  7 purchase totals = $1,131.86       $1,225.4925   $1,225.49   $1,225.50   $1,225.40