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	$40.69	12.349%	$45.7148	$45.71	$45.70	$45.70
Purchase #2	$153.44	12.411%	$172.4834	$172.48	$172.50	$172.50
Purchase #3	$93.71	5.732%	$99.0815	$99.08	$99.10	$99.10
Purchase #4	$143.97	11.679%	$160.7843	$160.78	$160.80	$160.80
Purchase #5	$138.40	9.184%	$151.1107	$151.11	$151.10	$151.10
Purchase #6	$19.60	4.127%	$20.4089	$20.41	$20.40	$20.40
Purchase #7	$20.56	8.485%	$22.3045	$22.30	$22.30	$22.30
7 purchase totals =	$610.37		$671.8881	$671.87	$671.90	$671.90