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	$227.76	13.493%	$258.4917	$258.49	$258.50	$258.50
Purchase #2	$71.27	9.615%	$78.1226	$78.12	$78.10	$78.10
Purchase #3	$153.61	12.468%	$172.7621	$172.76	$172.75	$172.80
Purchase #4	$208.70	7.865%	$225.1143	$225.11	$225.10	$225.10
Purchase #5	$53.97	10.314%	$59.5365	$59.54	$59.55	$59.50
Purchase #6	$140.29	8.276%	$151.9004	$151.90	$151.90	$151.90
Purchase #7	$185.60	10.254%	$204.6314	$204.63	$204.65	$204.60
7 purchase totals =	$1,041.20		$1,150.5590	$1,150.55	$1,150.55	$1,150.50