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 $89.68   13.313%   $101.6191   $101.62   $101.60   $101.60  
  Purchase #2 $42.65   8.494%   $46.2727   $46.27   $46.25   $46.30  
  Purchase #3 $165.27   7.488%   $177.6454   $177.65   $177.65   $177.60  
  Purchase #4 $131.97   12.532%   $148.5085   $148.51   $148.50   $148.50  
  Purchase #5 $48.56   4.288%   $50.6423   $50.64   $50.65   $50.60  
  Purchase #6 $153.74   4.473%   $160.6168   $160.62   $160.60   $160.60  
  Purchase #7 $91.43   10.513%   $101.042   $101.04   $101.05   $101.00  
  7 purchase totals = $723.30       $786.3468   $786.35   $786.30   $786.20