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 $248.54   10.181%   $273.8439   $273.84   $273.85   $273.80  
  Purchase #2 $94.75   9.327%   $103.5873   $103.59   $103.60   $103.60  
  Purchase #3 $109.88   12.541%   $123.6601   $123.66   $123.65   $123.70  
  Purchase #4 $118.41   3.176%   $122.1707   $122.17   $122.15   $122.20  
  Purchase #5 $244.53   9.815%   $268.5306   $268.53   $268.55   $268.50  
  Purchase #6 $44.64   7.508%   $47.9916   $47.99   $48.00   $48.00  
  Purchase #7 $205.76   10.572%   $227.5129   $227.51   $227.50   $227.50  
  7 purchase totals = $1,066.51       $1,167.2971   $1,167.29   $1,167.30   $1,167.30