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 $85.57   12.624%   $96.3724   $96.37   $96.35   $96.40  
  Purchase #2 $143.81   5.233%   $151.3356   $151.34   $151.35   $151.30  
  Purchase #3 $92.87   9.123%   $101.3425   $101.34   $101.35   $101.30  
  Purchase #4 $207.47   6.583%   $221.1278   $221.13   $221.15   $221.10  
  Purchase #5 $32.86   6.282%   $34.9243   $34.92   $34.90   $34.90  
  Purchase #6 $151.39   11.733%   $169.1526   $169.15   $169.15   $169.20  
  Purchase #7 $177.91   11.265%   $197.9516   $197.95   $197.95   $198.00  
  7 purchase totals = $891.88       $972.2068   $972.20   $972.20   $972.20