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	$166.78	3.333%	$172.3388	$172.34	$172.35	$172.30
Purchase #2	$228.28	11.563%	$254.676	$254.68	$254.70	$254.70
Purchase #3	$148.43	10.548%	$164.0864	$164.09	$164.10	$164.10
Purchase #4	$223.56	12.172%	$250.7717	$250.77	$250.75	$250.80
Purchase #5	$26.40	13.397%	$29.9368	$29.94	$29.95	$29.90
Purchase #6	$222.44	8.269%	$240.8336	$240.83	$240.85	$240.80
Purchase #7	$88.46	13.592%	$100.4835	$100.48	$100.50	$100.50
7 purchase totals =	$1,104.35		$1,213.1268	$1,213.13	$1,213.20	$1,213.10