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 $244.89   6.425%   $260.6242   $260.62   $260.60   $260.60  
  Purchase #2 $199.48   4.776%   $209.0072   $209.01   $209.00   $209.00  
  Purchase #3 $174.96   3.106%   $180.3943   $180.39   $180.40   $180.40  
  Purchase #4 $208.77   7.358%   $224.1313   $224.13   $224.15   $224.10  
  Purchase #5 $173.43   13.421%   $196.706   $196.71   $196.70   $196.70  
  Purchase #6 $233.97   12.827%   $263.9813   $263.98   $264.00   $264.00  
  Purchase #7 $26.77   11.827%   $29.9361   $29.94   $29.95   $29.90  
  7 purchase totals = $1,262.27       $1,364.7804   $1,364.78   $1,364.80   $1,364.70