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	$7.32	5.599%	$7.7298	$7.73	$7.75	$7.70
Purchase #2	$100.78	11.594%	$112.4644	$112.46	$112.45	$112.50
Purchase #3	$32.95	7.472%	$35.412	$35.41	$35.40	$35.40
Purchase #4	$239.34	12.248%	$268.6544	$268.65	$268.65	$268.70
Purchase #5	$51.44	8.175%	$55.6452	$55.65	$55.65	$55.60
Purchase #6	$105.78	10.137%	$116.5029	$116.50	$116.50	$116.50
Purchase #7	$45.62	9.407%	$49.9115	$49.91	$49.90	$49.90
7 purchase totals =	$583.23		$646.3202	$646.31	$646.30	$646.30