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 $244.91   6.213%   $260.1263   $260.13   $260.15   $260.10  
  Purchase #2 $125.88   8.718%   $136.8542   $136.85   $136.85   $136.90  
  Purchase #3 $69.95   13.510%   $79.4002   $79.40   $79.40   $79.40  
  Purchase #4 $168.84   8.296%   $182.847   $182.85   $182.85   $182.80  
  Purchase #5 $19.49   4.814%   $20.4282   $20.43   $20.45   $20.40  
  Purchase #6 $151.76   11.379%   $169.0288   $169.03   $169.05   $169.00  
  Purchase #7 $58.79   12.277%   $66.0076   $66.01   $66.00   $66.00  
  7 purchase totals = $839.62       $914.6923   $914.70   $914.75   $914.60