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	$35.67	5.134%	$37.5013	$37.50	$37.50	$37.50
Purchase #2	$243.85	10.612%	$269.7274	$269.73	$269.75	$269.70
Purchase #3	$151.84	5.309%	$159.9012	$159.90	$159.90	$159.90
Purchase #4	$59.56	4.208%	$62.0663	$62.07	$62.05	$62.10
Purchase #5	$45.29	13.220%	$51.2773	$51.28	$51.30	$51.30
Purchase #6	$117.39	13.490%	$133.2259	$133.23	$133.25	$133.20
Purchase #7	$151.52	9.252%	$165.5386	$165.54	$165.55	$165.50
7 purchase totals =	$805.12		$879.2380	$879.25	$879.30	$879.20