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 $230.70   4.564%   $241.2291   $241.23   $241.25   $241.20  
  Purchase #2 $62.63   8.742%   $68.1051   $68.11   $68.10   $68.10  
  Purchase #3 $71.82   8.485%   $77.9139   $77.91   $77.90   $77.90  
  Purchase #4 $11.93   6.811%   $12.7426   $12.74   $12.75   $12.70  
  Purchase #5 $244.78   3.661%   $253.7414   $253.74   $253.75   $253.70  
  Purchase #6 $40.28   10.509%   $44.513   $44.51   $44.50   $44.50  
  Purchase #7 $52.37   5.130%   $55.0566   $55.06   $55.05   $55.10  
  7 purchase totals = $714.51       $753.3017   $753.30   $753.30   $753.20