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 $82.27   12.581%   $92.6204   $92.62   $92.60   $92.60  
  Purchase #2 $175.30   5.676%   $185.25   $185.25   $185.25   $185.30  
  Purchase #3 $164.47   7.234%   $176.3678   $176.37   $176.35   $176.40  
  Purchase #4 $236.86   5.809%   $250.6192   $250.62   $250.60   $250.60  
  Purchase #5 $230.28   6.260%   $244.6955   $244.70   $244.70   $244.70  
  Purchase #6 $178.72   11.506%   $199.2835   $199.28   $199.30   $199.30  
  Purchase #7 $112.70   10.701%   $124.76   $124.76   $124.75   $124.80  
  7 purchase totals = $1,180.60       $1,273.5964   $1,273.60   $1,273.55   $1,273.70