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 $32.59   7.701%   $35.0998   $35.10   $35.10   $35.10  
  Purchase #2 $59.63   3.631%   $61.7952   $61.80   $61.80   $61.80  
  Purchase #3 $230.30   4.542%   $240.7602   $240.76   $240.75   $240.80  
  Purchase #4 $56.99   5.811%   $60.3017   $60.30   $60.30   $60.30  
  Purchase #5 $86.97   8.761%   $94.5894   $94.59   $94.60   $94.60  
  Purchase #6 $236.59   12.642%   $266.4997   $266.50   $266.50   $266.50  
  Purchase #7 $154.37   13.428%   $175.0988   $175.10   $175.10   $175.10  
  7 purchase totals = $857.44       $934.1448   $934.15   $934.15   $934.20