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	$42.88	13.386%	$48.6199	$48.62	$48.60	$48.60
Purchase #2	$35.91	3.150%	$37.0412	$37.04	$37.05	$37.00
Purchase #3	$124.83	13.857%	$142.1277	$142.13	$142.15	$142.10
Purchase #4	$95.79	7.147%	$102.6361	$102.64	$102.65	$102.60
Purchase #5	$9.92	3.742%	$10.2912	$10.29	$10.30	$10.30
Purchase #6	$87.30	3.867%	$90.6759	$90.68	$90.70	$90.70
Purchase #7	$10.95	4.220%	$11.4121	$11.41	$11.40	$11.40
7 purchase totals =	$407.58		$442.8041	$442.81	$442.85	$442.70