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	$6.54	7.854%	$7.0537	$7.05	$7.05	$7.10
Purchase #2	$110.73	8.204%	$119.8143	$119.81	$119.80	$119.80
Purchase #3	$63.78	10.251%	$70.3181	$70.32	$70.30	$70.30
Purchase #4	$83.50	8.671%	$90.7403	$90.74	$90.75	$90.70
Purchase #5	$151.82	3.795%	$157.5816	$157.58	$157.60	$157.60
Purchase #6	$101.81	9.533%	$111.5155	$111.52	$111.50	$111.50
Purchase #7	$137.38	10.864%	$152.305	$152.31	$152.30	$152.30
7 purchase totals =	$655.56		$709.3285	$709.33	$709.30	$709.30