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 $133.36   7.104%   $142.8339   $142.83   $142.85   $142.80  
  Purchase #2 $75.25   5.462%   $79.3602   $79.36   $79.35   $79.40  
  Purchase #3 $69.29   13.593%   $78.7086   $78.71   $78.70   $78.70  
  Purchase #4 $245.46   6.125%   $260.4944   $260.49   $260.50   $260.50  
  Purchase #5 $89.30   9.598%   $97.871   $97.87   $97.85   $97.90  
  Purchase #6 $152.65   13.578%   $173.3768   $173.38   $173.40   $173.40  
  Purchase #7 $200.58   8.555%   $217.7396   $217.74   $217.75   $217.70  
  7 purchase totals = $965.89       $1,050.3845   $1,050.38   $1,050.40   $1,050.40