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 $28.91   13.158%   $32.714   $32.71   $32.70   $32.70  
  Purchase #2 $240.86   12.741%   $271.548   $271.55   $271.55   $271.50  
  Purchase #3 $193.68   6.160%   $205.6107   $205.61   $205.60   $205.60  
  Purchase #4 $168.28   5.504%   $177.5421   $177.54   $177.55   $177.50  
  Purchase #5 $180.67   8.762%   $196.5003   $196.50   $196.50   $196.50  
  Purchase #6 $203.55   7.733%   $219.2905   $219.29   $219.30   $219.30  
  Purchase #7 $233.41   9.521%   $255.633   $255.63   $255.65   $255.60  
  7 purchase totals = $1,249.36       $1,358.8386   $1,358.83   $1,358.85   $1,358.70