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 $7.46   6.600%   $7.9524   $7.95   $7.95   $8.00  
  Purchase #2 $28.47   7.212%   $30.5233   $30.52   $30.50   $30.50  
  Purchase #3 $120.72   12.872%   $136.2591   $136.26   $136.25   $136.30  
  Purchase #4 $217.61   12.159%   $244.0692   $244.07   $244.05   $244.10  
  Purchase #5 $105.83   8.763%   $115.1039   $115.10   $115.10   $115.10  
  Purchase #6 $144.61   9.584%   $158.4694   $158.47   $158.45   $158.50  
  Purchase #7 $215.91   3.326%   $223.0912   $223.09   $223.10   $223.10  
  7 purchase totals = $840.61       $915.4685   $915.46   $915.40   $915.60