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	$61.51	8.748%	$66.8909	$66.89	$66.90	$66.90
Purchase #2	$154.33	11.653%	$172.3141	$172.31	$172.30	$172.30
Purchase #3	$48.62	5.738%	$51.4098	$51.41	$51.40	$51.40
Purchase #4	$246.87	13.115%	$279.247	$279.25	$279.25	$279.20
Purchase #5	$218.93	11.552%	$244.2208	$244.22	$244.20	$244.20
Purchase #6	$5.71	4.650%	$5.9755	$5.98	$6.00	$6.00
Purchase #7	$250.92	5.302%	$264.2238	$264.22	$264.20	$264.20
7 purchase totals =	$986.89		$1,084.2819	$1,084.28	$1,084.25	$1,084.20