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	$238.48	12.233%	$267.6533	$267.65	$267.65	$267.70
Purchase #2	$155.61	11.806%	$173.9813	$173.98	$174.00	$174.00
Purchase #3	$118.93	7.512%	$127.864	$127.86	$127.85	$127.90
Purchase #4	$56.54	8.657%	$61.4347	$61.43	$61.45	$61.40
Purchase #5	$81.93	9.646%	$89.833	$89.83	$89.85	$89.80
Purchase #6	$230.83	6.796%	$246.5172	$246.52	$246.50	$246.50
Purchase #7	$33.88	4.404%	$35.3721	$35.37	$35.35	$35.40
7 purchase totals =	$916.20		$1,002.6556	$1,002.64	$1,002.65	$1,002.70