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 $244.64   12.824%   $276.0126   $276.01   $276.00   $276.00  
  Purchase #2 $112.95   11.223%   $125.6264   $125.63   $125.65   $125.60  
  Purchase #3 $213.91   3.358%   $221.0931   $221.09   $221.10   $221.10  
  Purchase #4 $187.76   4.178%   $195.6046   $195.60   $195.60   $195.60  
  Purchase #5 $184.68   13.384%   $209.3976   $209.40   $209.40   $209.40  
  Purchase #6 $75.45   7.597%   $81.1819   $81.18   $81.20   $81.20  
  Purchase #7 $61.87   7.457%   $66.4836   $66.48   $66.50   $66.50  
  7 purchase totals = $1,081.26       $1,175.3998   $1,175.39   $1,175.45   $1,175.40