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	$37.66	7.543%	$40.5007	$40.50	$40.50	$40.50
Purchase #2	$82.58	5.462%	$87.0905	$87.09	$87.10	$87.10
Purchase #3	$235.58	5.632%	$248.8479	$248.85	$248.85	$248.80
Purchase #4	$89.29	12.164%	$100.1512	$100.15	$100.15	$100.20
Purchase #5	$232.80	13.450%	$264.1116	$264.11	$264.10	$264.10
Purchase #6	$20.73	10.444%	$22.895	$22.90	$22.90	$22.90
Purchase #7	$117.54	8.501%	$127.5321	$127.53	$127.55	$127.50
7 purchase totals =	$816.18		$891.1290	$891.13	$891.15	$891.10