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 $56.69   9.287%   $61.9548   $61.95   $61.95   $62.00  
  Purchase #2 $110.43   8.569%   $119.8927   $119.89   $119.90   $119.90  
  Purchase #3 $211.63   4.123%   $220.3555   $220.36   $220.35   $220.40  
  Purchase #4 $35.87   9.170%   $39.1593   $39.16   $39.15   $39.20  
  Purchase #5 $242.73   4.380%   $253.3616   $253.36   $253.35   $253.40  
  Purchase #6 $170.87   9.682%   $187.4136   $187.41   $187.40   $187.40  
  Purchase #7 $59.80   3.444%   $61.8595   $61.86   $61.85   $61.90  
  7 purchase totals = $888.02       $943.9970   $943.99   $943.95   $944.20