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	$240.42	6.349%	$255.6843	$255.68	$255.70	$255.70
Purchase #2	$45.31	13.123%	$51.256	$51.26	$51.25	$51.30
Purchase #3	$247.92	3.208%	$255.8733	$255.87	$255.85	$255.90
Purchase #4	$249.26	4.823%	$261.2818	$261.28	$261.30	$261.30
Purchase #5	$91.48	5.313%	$96.3403	$96.34	$96.35	$96.30
Purchase #6	$176.92	12.185%	$198.4777	$198.48	$198.50	$198.50
Purchase #7	$200.67	11.150%	$223.0447	$223.04	$223.05	$223.00
7 purchase totals =	$1,251.98		$1,341.9581	$1,341.95	$1,342.00	$1,342.00