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	$48.62	5.502%	$51.2951	$51.30	$51.30	$51.30
Purchase #2	$108.90	12.119%	$122.0976	$122.10	$122.10	$122.10
Purchase #3	$135.95	11.268%	$151.2688	$151.27	$151.25	$151.30
Purchase #4	$111.79	10.283%	$123.2854	$123.29	$123.30	$123.30
Purchase #5	$187.51	10.188%	$206.6135	$206.61	$206.60	$206.60
Purchase #6	$83.50	10.766%	$92.4896	$92.49	$92.50	$92.50
Purchase #7	$30.61	8.330%	$33.1598	$33.16	$33.15	$33.20
7 purchase totals =	$706.88		$780.2098	$780.22	$780.20	$780.30