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   13.650%   $59.6776   $59.68   $59.70   $59.70  
  Purchase #2 $195.28   5.140%   $205.3174   $205.32   $205.30   $205.30  
  Purchase #3 $35.34   10.624%   $39.0945   $39.09   $39.10   $39.10  
  Purchase #4 $107.91   10.653%   $119.4057   $119.41   $119.40   $119.40  
  Purchase #5 $78.43   3.258%   $80.9852   $80.99   $81.00   $81.00  
  Purchase #6 $167.35   13.359%   $189.7063   $189.71   $189.70   $189.70  
  Purchase #7 $219.55   13.719%   $249.6701   $249.67   $249.65   $249.70  
  7 purchase totals = $856.37       $943.8568   $943.87   $943.85   $943.90