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	$64.89	12.344%	$72.9	$72.90	$72.90	$72.90
Purchase #2	$165.54	3.466%	$171.2776	$171.28	$171.30	$171.30
Purchase #3	$52.78	5.867%	$55.8766	$55.88	$55.90	$55.90
Purchase #4	$196.57	4.485%	$205.3862	$205.39	$205.40	$205.40
Purchase #5	$113.32	13.499%	$128.6171	$128.62	$128.60	$128.60
Purchase #6	$237.77	9.600%	$260.5959	$260.60	$260.60	$260.60
Purchase #7	$231.54	11.845%	$258.9659	$258.97	$258.95	$259.00
7 purchase totals =	$1,062.41		$1,153.6193	$1,153.64	$1,153.65	$1,153.70