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 $68.26   12.252%   $76.6232   $76.62   $76.60   $76.60  
  Purchase #2 $29.28   11.397%   $32.617   $32.62   $32.60   $32.60  
  Purchase #3 $164.85   8.400%   $178.6974   $178.70   $178.70   $178.70  
  Purchase #4 $28.25   7.231%   $30.2928   $30.29   $30.30   $30.30  
  Purchase #5 $181.87   6.389%   $193.4897   $193.49   $193.50   $193.50  
  Purchase #6 $162.55   13.687%   $184.7982   $184.80   $184.80   $184.80  
  Purchase #7 $246.82   10.246%   $272.1092   $272.11   $272.10   $272.10  
  7 purchase totals = $881.88       $968.6275   $968.63   $968.60   $968.60