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	$86.49	5.482%	$91.2314	$91.23	$91.25	$91.20
Purchase #2	$108.36	8.407%	$117.4698	$117.47	$117.45	$117.50
Purchase #3	$191.75	8.381%	$207.8206	$207.82	$207.80	$207.80
Purchase #4	$38.83	9.278%	$42.4326	$42.43	$42.45	$42.40
Purchase #5	$227.86	10.277%	$251.2772	$251.28	$251.30	$251.30
Purchase #6	$190.42	5.429%	$200.7579	$200.76	$200.75	$200.80
Purchase #7	$40.67	3.594%	$42.1317	$42.13	$42.15	$42.10
7 purchase totals =	$884.38		$953.1212	$953.12	$953.15	$953.10