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 $249.74   10.602%   $276.2174   $276.22   $276.20   $276.20  
  Purchase #2 $248.51   5.240%   $261.5319   $261.53   $261.55   $261.50  
  Purchase #3 $68.82   9.848%   $75.5974   $75.60   $75.60   $75.60  
  Purchase #4 $138.83   9.187%   $151.5843   $151.58   $151.60   $151.60  
  Purchase #5 $43.58   12.272%   $48.9281   $48.93   $48.95   $48.90  
  Purchase #6 $190.43   3.454%   $197.0075   $197.01   $197.00   $197.00  
  Purchase #7 $191.57   6.523%   $204.0661   $204.07   $204.05   $204.10  
  7 purchase totals = $1,131.48       $1,214.9327   $1,214.94   $1,214.95   $1,214.90