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	$37.65	12.249%	$42.2617	$42.26	$42.25	$42.30
Purchase #2	$91.93	4.662%	$96.2158	$96.22	$96.20	$96.20
Purchase #3	$197.47	12.464%	$222.0827	$222.08	$222.10	$222.10
Purchase #4	$49.52	13.269%	$56.0908	$56.09	$56.10	$56.10
Purchase #5	$159.68	12.641%	$179.8651	$179.87	$179.85	$179.90
Purchase #6	$217.52	5.292%	$229.0312	$229.03	$229.05	$229.00
Purchase #7	$157.25	10.869%	$174.3415	$174.34	$174.35	$174.30
7 purchase totals =	$911.02		$999.8888	$999.89	$999.90	$999.90