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	$61.71	7.294%	$66.2111	$66.21	$66.20	$66.20
Purchase #2	$128.38	12.550%	$144.4917	$144.49	$144.50	$144.50
Purchase #3	$62.34	13.830%	$70.9616	$70.96	$70.95	$71.00
Purchase #4	$210.25	11.148%	$233.6887	$233.69	$233.70	$233.70
Purchase #5	$212.26	12.247%	$238.2555	$238.26	$238.25	$238.30
Purchase #6	$111.38	6.439%	$118.5518	$118.55	$118.55	$118.60
Purchase #7	$221.91	5.185%	$233.416	$233.42	$233.40	$233.40
7 purchase totals =	$1,008.23		$1,105.5764	$1,105.58	$1,105.55	$1,105.70