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	$42.72	6.809%	$45.6288	$45.63	$45.65	$45.60
Purchase #2	$46.61	10.239%	$51.3824	$51.38	$51.40	$51.40
Purchase #3	$222.69	13.870%	$253.5771	$253.58	$253.60	$253.60
Purchase #4	$24.89	3.765%	$25.8271	$25.83	$25.85	$25.80
Purchase #5	$70.67	10.799%	$78.3017	$78.30	$78.30	$78.30
Purchase #6	$156.58	10.208%	$172.5637	$172.56	$172.55	$172.60
Purchase #7	$106.63	4.549%	$111.4806	$111.48	$111.50	$111.50
7 purchase totals =	$670.79		$738.7614	$738.76	$738.85	$738.80