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	$34.57	9.379%	$37.8123	$37.81	$37.80	$37.80
Purchase #2	$250.78	11.464%	$279.5294	$279.53	$279.55	$279.50
Purchase #3	$92.72	13.778%	$105.495	$105.50	$105.50	$105.50
Purchase #4	$230.81	7.808%	$248.8316	$248.83	$248.85	$248.80
Purchase #5	$146.78	7.542%	$157.8501	$157.85	$157.85	$157.90
Purchase #6	$171.97	8.363%	$186.3519	$186.35	$186.35	$186.40
Purchase #7	$149.55	11.173%	$166.2592	$166.26	$166.25	$166.30
7 purchase totals =	$1,077.18		$1,182.1295	$1,182.13	$1,182.15	$1,182.20