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 $244.88   9.113%   $267.1959   $267.20   $267.20   $267.20  
  Purchase #2 $50.95   9.683%   $55.8835   $55.88   $55.90   $55.90  
  Purchase #3 $51.63   11.648%   $57.6439   $57.64   $57.65   $57.60  
  Purchase #4 $249.80   5.405%   $263.3017   $263.30   $263.30   $263.30  
  Purchase #5 $116.53   10.323%   $128.5594   $128.56   $128.55   $128.60  
  Purchase #6 $241.90   8.592%   $262.684   $262.68   $262.70   $262.70  
  Purchase #7 $160.37   11.286%   $178.4694   $178.47   $178.45   $178.50  
  7 purchase totals = $1,116.06       $1,213.7378   $1,213.73   $1,213.75   $1,213.80