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	$172.36	7.592%	$185.4456	$185.45	$185.45	$185.40
Purchase #2	$146.72	13.572%	$166.6328	$166.63	$166.65	$166.60
Purchase #3	$109.53	6.616%	$116.7765	$116.78	$116.80	$116.80
Purchase #4	$118.27	5.369%	$124.6199	$124.62	$124.60	$124.60
Purchase #5	$40.35	3.817%	$41.8902	$41.89	$41.90	$41.90
Purchase #6	$162.45	13.372%	$184.1728	$184.17	$184.15	$184.20
Purchase #7	$66.93	7.677%	$72.0682	$72.07	$72.05	$72.10
7 purchase totals =	$816.61		$891.6060	$891.61	$891.60	$891.60