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 $203.83   3.493%   $210.9498   $210.95   $210.95   $210.90  
  Purchase #2 $120.74   11.188%   $134.2484   $134.25   $134.25   $134.20  
  Purchase #3 $176.70   7.794%   $190.472   $190.47   $190.45   $190.50  
  Purchase #4 $34.52   6.591%   $36.7952   $36.80   $36.80   $36.80  
  Purchase #5 $107.30   8.258%   $116.1608   $116.16   $116.15   $116.20  
  Purchase #6 $236.73   12.733%   $266.8728   $266.87   $266.85   $266.90  
  Purchase #7 $76.30   6.473%   $81.2389   $81.24   $81.25   $81.20  
  7 purchase totals = $956.12       $1,036.7379   $1,036.74   $1,036.70   $1,036.70