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	$37.85	3.831%	$39.3	$39.30	$39.30	$39.30
Purchase #2	$58.71	3.836%	$60.9621	$60.96	$60.95	$61.00
Purchase #3	$100.64	10.825%	$111.5343	$111.53	$111.55	$111.50
Purchase #4	$157.71	4.343%	$164.5593	$164.56	$164.55	$164.60
Purchase #5	$122.85	6.290%	$130.5773	$130.58	$130.60	$130.60
Purchase #6	$70.28	9.470%	$76.9355	$76.94	$76.95	$76.90
Purchase #7	$74.31	12.813%	$83.8313	$83.83	$83.85	$83.80
7 purchase totals =	$622.35		$667.6998	$667.70	$667.75	$667.70