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 $76.46   8.494%   $82.9545   $82.95   $82.95   $83.00  
  Purchase #2 $104.57   11.848%   $116.9595   $116.96   $116.95   $117.00  
  Purchase #3 $85.75   10.420%   $94.6852   $94.69   $94.70   $94.70  
  Purchase #4 $134.68   13.728%   $153.1689   $153.17   $153.15   $153.20  
  Purchase #5 $198.41   13.155%   $224.5108   $224.51   $224.50   $224.50  
  Purchase #6 $22.69   11.823%   $25.3726   $25.37   $25.35   $25.40  
  Purchase #7 $206.78   8.858%   $225.0966   $225.10   $225.10   $225.10  
  7 purchase totals = $829.34       $922.7481   $922.75   $922.70   $922.90