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 $64.82   6.523%   $69.0482   $69.05   $69.05   $69.00  
  Purchase #2 $118.89   10.836%   $131.7729   $131.77   $131.75   $131.80  
  Purchase #3 $27.93   8.494%   $30.3024   $30.30   $30.30   $30.30  
  Purchase #4 $139.99   3.540%   $144.9456   $144.95   $144.95   $144.90  
  Purchase #5 $233.57   11.457%   $260.3301   $260.33   $260.35   $260.30  
  Purchase #6 $9.50   13.294%   $10.7629   $10.76   $10.75   $10.80  
  Purchase #7 $105.82   10.308%   $116.7279   $116.73   $116.75   $116.70  
  7 purchase totals = $700.52       $763.8900   $763.89   $763.90   $763.80