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	$159.50	6.221%	$169.4225	$169.42	$169.40	$169.40
Purchase #2	$126.37	3.251%	$130.4783	$130.48	$130.50	$130.50
Purchase #3	$142.68	8.817%	$155.2601	$155.26	$155.25	$155.30
Purchase #4	$30.85	4.669%	$32.2904	$32.29	$32.30	$32.30
Purchase #5	$74.81	9.409%	$81.8489	$81.85	$81.85	$81.80
Purchase #6	$92.93	7.767%	$100.1479	$100.15	$100.15	$100.10
Purchase #7	$34.78	8.175%	$37.6233	$37.62	$37.60	$37.60
7 purchase totals =	$661.92		$707.0714	$707.07	$707.05	$707.00