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 $55.37   13.219%   $62.6894   $62.69   $62.70   $62.70  
  Purchase #2 $189.49   3.225%   $195.6011   $195.60   $195.60   $195.60  
  Purchase #3 $7.73   12.220%   $8.6746   $8.67   $8.65   $8.70  
  Purchase #4 $69.26   7.161%   $74.2197   $74.22   $74.20   $74.20  
  Purchase #5 $208.34   4.582%   $217.8861   $217.89   $217.90   $217.90  
  Purchase #6 $169.40   3.453%   $175.2494   $175.25   $175.25   $175.20  
  Purchase #7 $54.91   10.394%   $60.6173   $60.62   $60.60   $60.60  
  7 purchase totals = $754.50       $794.9376   $794.94   $794.90   $794.90