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	$10.82	4.462%	$11.3028	$11.30	$11.30	$11.30
Purchase #2	$126.60	13.668%	$143.9037	$143.90	$143.90	$143.90
Purchase #3	$137.86	7.805%	$148.62	$148.62	$148.60	$148.60
Purchase #4	$103.81	11.762%	$116.0201	$116.02	$116.00	$116.00
Purchase #5	$41.53	9.653%	$45.5389	$45.54	$45.55	$45.50
Purchase #6	$31.91	10.121%	$35.1396	$35.14	$35.15	$35.10
Purchase #7	$44.90	11.519%	$50.072	$50.07	$50.05	$50.10
7 purchase totals =	$497.43		$550.5971	$550.59	$550.55	$550.50