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 $249.63   6.553%   $265.9883   $265.99   $266.00   $266.00  
  Purchase #2 $60.78   13.702%   $69.1081   $69.11   $69.10   $69.10  
  Purchase #3 $209.82   6.741%   $223.964   $223.96   $223.95   $224.00  
  Purchase #4 $87.44   9.782%   $95.9934   $95.99   $96.00   $96.00  
  Purchase #5 $52.50   6.465%   $55.8941   $55.89   $55.90   $55.90  
  Purchase #6 $6.54   10.618%   $7.2344   $7.23   $7.25   $7.20  
  Purchase #7 $228.59   7.498%   $245.7297   $245.73   $245.75   $245.70  
  7 purchase totals = $895.30       $963.9120   $963.90   $963.95   $963.90