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	$78.61	3.690%	$81.5107	$81.51	$81.50	$81.50
Purchase #2	$102.91	8.400%	$111.5544	$111.55	$111.55	$111.60
Purchase #3	$26.76	13.700%	$30.4261	$30.43	$30.45	$30.40
Purchase #4	$126.47	3.249%	$130.579	$130.58	$130.60	$130.60
Purchase #5	$130.58	4.281%	$136.1701	$136.17	$136.15	$136.20
Purchase #6	$155.54	7.102%	$166.5865	$166.59	$166.60	$166.60
Purchase #7	$111.34	8.307%	$120.589	$120.59	$120.60	$120.60
7 purchase totals =	$732.21		$777.4158	$777.42	$777.45	$777.50