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	$246.70	13.553%	$280.1353	$280.14	$280.15	$280.10
Purchase #2	$146.31	4.609%	$153.0534	$153.05	$153.05	$153.10
Purchase #3	$136.73	11.631%	$152.6331	$152.63	$152.65	$152.60
Purchase #4	$121.41	4.782%	$127.2158	$127.22	$127.20	$127.20
Purchase #5	$131.35	3.758%	$136.2861	$136.29	$136.30	$136.30
Purchase #6	$34.94	6.199%	$37.1059	$37.11	$37.10	$37.10
Purchase #7	$27.46	8.726%	$29.8562	$29.86	$29.85	$29.90
7 purchase totals =	$844.90		$916.2858	$916.30	$916.30	$916.30