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	$34.51	10.628%	$38.1777	$38.18	$38.20	$38.20
Purchase #2	$158.89	3.635%	$164.6657	$164.67	$164.65	$164.70
Purchase #3	$63.27	12.377%	$71.1009	$71.10	$71.10	$71.10
Purchase #4	$66.69	9.853%	$73.261	$73.26	$73.25	$73.30
Purchase #5	$229.71	5.836%	$243.1159	$243.12	$243.10	$243.10
Purchase #6	$58.74	10.510%	$64.9136	$64.91	$64.90	$64.90
Purchase #7	$11.51	8.699%	$12.5113	$12.51	$12.50	$12.50
7 purchase totals =	$623.32		$667.7461	$667.75	$667.70	$667.80