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	$182.40	7.678%	$196.4047	$196.40	$196.40	$196.40
Purchase #2	$33.28	6.352%	$35.3939	$35.39	$35.40	$35.40
Purchase #3	$32.79	7.337%	$35.1958	$35.20	$35.20	$35.20
Purchase #4	$231.81	3.681%	$240.3429	$240.34	$240.35	$240.30
Purchase #5	$24.90	10.574%	$27.5329	$27.53	$27.55	$27.50
Purchase #6	$72.31	13.167%	$81.8311	$81.83	$81.85	$81.80
Purchase #7	$40.46	8.410%	$43.8627	$43.86	$43.85	$43.90
7 purchase totals =	$617.95		$660.5640	$660.55	$660.60	$660.50