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	$230.29	3.738%	$238.8982	$238.90	$238.90	$238.90
Purchase #2	$135.27	11.679%	$151.0682	$151.07	$151.05	$151.10
Purchase #3	$112.88	8.572%	$122.5561	$122.56	$122.55	$122.60
Purchase #4	$209.46	11.759%	$234.0904	$234.09	$234.10	$234.10
Purchase #5	$55.77	10.680%	$61.7262	$61.73	$61.75	$61.70
Purchase #6	$172.36	7.850%	$185.8903	$185.89	$185.90	$185.90
Purchase #7	$152.53	12.286%	$171.2698	$171.27	$171.25	$171.30
7 purchase totals =	$1,068.56		$1,165.4992	$1,165.51	$1,165.50	$1,165.60