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 $242.86   10.513%   $268.3919   $268.39   $268.40   $268.40  
  Purchase #2 $93.35   4.227%   $97.2959   $97.30   $97.30   $97.30  
  Purchase #3 $220.95   10.721%   $244.638   $244.64   $244.65   $244.60  
  Purchase #4 $75.39   13.727%   $85.7388   $85.74   $85.75   $85.70  
  Purchase #5 $134.76   3.763%   $139.831   $139.83   $139.85   $139.80  
  Purchase #6 $8.38   3.600%   $8.6817   $8.68   $8.70   $8.70  
  Purchase #7 $74.92   10.438%   $82.7401   $82.74   $82.75   $82.70  
  7 purchase totals = $850.61       $927.3174   $927.32   $927.40   $927.20