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	$243.57	12.610%	$274.2842	$274.28	$274.30	$274.30
Purchase #2	$239.70	6.532%	$255.3572	$255.36	$255.35	$255.40
Purchase #3	$40.26	12.317%	$45.2188	$45.22	$45.20	$45.20
Purchase #4	$61.37	13.457%	$69.6286	$69.63	$69.65	$69.60
Purchase #5	$116.89	9.310%	$127.7725	$127.77	$127.75	$127.80
Purchase #6	$37.56	13.146%	$42.4976	$42.50	$42.50	$42.50
Purchase #7	$94.28	4.530%	$98.5509	$98.55	$98.55	$98.60
7 purchase totals =	$833.63		$913.3098	$913.31	$913.30	$913.40