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	$222.88	12.311%	$250.3188	$250.32	$250.30	$250.30
Purchase #2	$50.74	6.253%	$53.9128	$53.91	$53.90	$53.90
Purchase #3	$74.96	10.784%	$83.0437	$83.04	$83.05	$83.00
Purchase #4	$83.87	11.150%	$93.2215	$93.22	$93.20	$93.20
Purchase #5	$61.91	8.821%	$67.3711	$67.37	$67.35	$67.40
Purchase #6	$30.93	3.174%	$31.9117	$31.91	$31.90	$31.90
Purchase #7	$203.94	9.589%	$223.4958	$223.50	$223.50	$223.50
7 purchase totals =	$729.23		$803.2754	$803.27	$803.20	$803.20