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 $241.41   6.427%   $256.9254   $256.93   $256.95   $256.90  
  Purchase #2 $66.37   10.407%   $73.2771   $73.28   $73.30   $73.30  
  Purchase #3 $248.37   11.477%   $276.8754   $276.88   $276.90   $276.90  
  Purchase #4 $93.87   4.225%   $97.836   $97.84   $97.85   $97.80  
  Purchase #5 $222.28   7.660%   $239.3066   $239.31   $239.30   $239.30  
  Purchase #6 $197.57   4.391%   $206.2453   $206.25   $206.25   $206.20  
  Purchase #7 $224.49   4.330%   $234.2104   $234.21   $234.20   $234.20  
  7 purchase totals = $1,294.36       $1,384.6762   $1,384.70   $1,384.75   $1,384.60