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	$141.48	13.171%	$160.1143	$160.11	$160.10	$160.10
Purchase #2	$102.68	8.456%	$111.3626	$111.36	$111.35	$111.40
Purchase #3	$185.50	6.140%	$196.8897	$196.89	$196.90	$196.90
Purchase #4	$53.90	10.599%	$59.6129	$59.61	$59.60	$59.60
Purchase #5	$71.68	6.120%	$76.0668	$76.07	$76.05	$76.10
Purchase #6	$116.99	9.203%	$127.7566	$127.76	$127.75	$127.80
Purchase #7	$74.41	6.858%	$79.513	$79.51	$79.50	$79.50
7 purchase totals =	$746.64		$811.3159	$811.31	$811.25	$811.40