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	$34.84	8.845%	$37.9216	$37.92	$37.90	$37.90
Purchase #2	$196.66	4.403%	$205.3189	$205.32	$205.30	$205.30
Purchase #3	$158.49	5.827%	$167.7252	$167.73	$167.75	$167.70
Purchase #4	$23.39	12.242%	$26.2534	$26.25	$26.25	$26.30
Purchase #5	$178.27	7.420%	$191.4976	$191.50	$191.50	$191.50
Purchase #6	$6.93	5.176%	$7.2887	$7.29	$7.30	$7.30
Purchase #7	$133.45	11.300%	$148.5299	$148.53	$148.55	$148.50
7 purchase totals =	$732.03		$784.5353	$784.54	$784.55	$784.50