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	$244.41	5.796%	$258.576	$258.58	$258.60	$258.60
Purchase #2	$54.49	9.668%	$59.7581	$59.76	$59.75	$59.80
Purchase #3	$40.67	11.287%	$45.2604	$45.26	$45.25	$45.30
Purchase #4	$145.72	8.766%	$158.4938	$158.49	$158.50	$158.50
Purchase #5	$188.65	9.587%	$206.7359	$206.74	$206.75	$206.70
Purchase #6	$45.61	3.402%	$47.1617	$47.16	$47.15	$47.20
Purchase #7	$69.74	8.666%	$75.7837	$75.78	$75.80	$75.80
7 purchase totals =	$789.29		$851.7696	$851.77	$851.80	$851.90