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 $52.51   12.376%   $59.0086   $59.01   $59.00   $59.00  
  Purchase #2 $179.90   5.122%   $189.1145   $189.11   $189.10   $189.10  
  Purchase #3 $221.54   9.106%   $241.7134   $241.71   $241.70   $241.70  
  Purchase #4 $245.45   6.733%   $261.9761   $261.98   $262.00   $262.00  
  Purchase #5 $170.47   3.725%   $176.82   $176.82   $176.80   $176.80  
  Purchase #6 $18.64   8.663%   $20.2548   $20.25   $20.25   $20.30  
  Purchase #7 $156.65   10.641%   $173.3191   $173.32   $173.30   $173.30  
  7 purchase totals = $1,045.16       $1,122.2065   $1,122.20   $1,122.15   $1,122.20