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 $62.73   3.614%   $64.9971   $65.00   $65.00   $65.00  
  Purchase #2 $82.98   5.452%   $87.5041   $87.50   $87.50   $87.50  
  Purchase #3 $116.32   10.239%   $128.23   $128.23   $128.25   $128.20  
  Purchase #4 $238.92   6.191%   $253.7115   $253.71   $253.70   $253.70  
  Purchase #5 $60.59   7.296%   $65.0106   $65.01   $65.00   $65.00  
  Purchase #6 $148.86   8.252%   $161.1439   $161.14   $161.15   $161.10  
  Purchase #7 $203.41   5.349%   $214.2904   $214.29   $214.30   $214.30  
  7 purchase totals = $913.81       $974.8876   $974.88   $974.90   $974.80