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 $229.57   8.733%   $249.6183   $249.62   $249.60   $249.60  
  Purchase #2 $226.97   9.841%   $249.3061   $249.31   $249.30   $249.30  
  Purchase #3 $58.93   11.135%   $65.4919   $65.49   $65.50   $65.50  
  Purchase #4 $18.87   3.545%   $19.5389   $19.54   $19.55   $19.50  
  Purchase #5 $173.90   12.358%   $195.3906   $195.39   $195.40   $195.40  
  Purchase #6 $77.75   9.317%   $84.994   $84.99   $85.00   $85.00  
  Purchase #7 $232.84   9.762%   $255.5698   $255.57   $255.55   $255.60  
  7 purchase totals = $1,018.83       $1,119.9096   $1,119.91   $1,119.90   $1,119.90