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 $188.32   4.211%   $196.2502   $196.25   $196.25   $196.30  
  Purchase #2 $174.49   5.736%   $184.4987   $184.50   $184.50   $184.50  
  Purchase #3 $195.48   8.597%   $212.2854   $212.29   $212.30   $212.30  
  Purchase #4 $239.77   11.708%   $267.8423   $267.84   $267.85   $267.80  
  Purchase #5 $202.62   5.191%   $213.138   $213.14   $213.15   $213.10  
  Purchase #6 $249.34   5.733%   $263.6347   $263.63   $263.65   $263.60  
  Purchase #7 $59.81   11.470%   $66.6702   $66.67   $66.65   $66.70  
  7 purchase totals = $1,309.83       $1,404.3195   $1,404.32   $1,404.35   $1,404.30