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	$19.66	9.632%	$21.5537	$21.55	$21.55	$21.60
Purchase #2	$35.28	13.568%	$40.0668	$40.07	$40.05	$40.10
Purchase #3	$89.96	8.603%	$97.6993	$97.70	$97.70	$97.70
Purchase #4	$153.71	4.459%	$160.5639	$160.56	$160.55	$160.60
Purchase #5	$188.45	4.336%	$196.6212	$196.62	$196.60	$196.60
Purchase #6	$149.42	12.605%	$168.2544	$168.25	$168.25	$168.30
Purchase #7	$119.30	9.636%	$130.7957	$130.80	$130.80	$130.80
7 purchase totals =	$755.78		$815.5550	$815.55	$815.50	$815.70