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 $218.69   10.428%   $241.495   $241.50   $241.50   $241.50  
  Purchase #2 $91.98   6.210%   $97.692   $97.69   $97.70   $97.70  
  Purchase #3 $154.80   13.846%   $176.2336   $176.23   $176.25   $176.20  
  Purchase #4 $108.65   4.675%   $113.7294   $113.73   $113.75   $113.70  
  Purchase #5 $20.75   12.701%   $23.3855   $23.39   $23.40   $23.40  
  Purchase #6 $142.89   3.710%   $148.1912   $148.19   $148.20   $148.20  
  Purchase #7 $137.50   13.705%   $156.3444   $156.34   $156.35   $156.30  
  7 purchase totals = $875.26       $957.0711   $957.07   $957.15   $957.00