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 $242.37   7.383%   $260.2642   $260.26   $260.25   $260.30  
  Purchase #2 $171.37   13.210%   $194.008   $194.01   $194.00   $194.00  
  Purchase #3 $53.31   11.609%   $59.4988   $59.50   $59.50   $59.50  
  Purchase #4 $97.98   3.302%   $101.2153   $101.22   $101.20   $101.20  
  Purchase #5 $51.75   11.806%   $57.8596   $57.86   $57.85   $57.90  
  Purchase #6 $75.99   12.210%   $85.2684   $85.27   $85.25   $85.30  
  Purchase #7 $129.55   4.781%   $135.7438   $135.74   $135.75   $135.70  
  7 purchase totals = $822.32       $893.8581   $893.86   $893.80   $893.90