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 $217.27   13.790%   $247.2315   $247.23   $247.25   $247.20  
  Purchase #2 $88.66   10.395%   $97.8762   $97.88   $97.90   $97.90  
  Purchase #3 $56.33   4.199%   $58.6953   $58.70   $58.70   $58.70  
  Purchase #4 $199.73   4.343%   $208.4043   $208.40   $208.40   $208.40  
  Purchase #5 $181.59   7.489%   $195.1893   $195.19   $195.20   $195.20  
  Purchase #6 $76.65   6.315%   $81.4904   $81.49   $81.50   $81.50  
  Purchase #7 $18.51   13.807%   $21.0657   $21.07   $21.05   $21.10  
  7 purchase totals = $838.74       $909.9527   $909.96   $910.00   $910.00