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	$37.26	13.278%	$42.2074	$42.21	$42.20	$42.20
Purchase #2	$209.67	6.869%	$224.0722	$224.07	$224.05	$224.10
Purchase #3	$103.61	7.492%	$111.3725	$111.37	$111.35	$111.40
Purchase #4	$176.84	7.463%	$190.0376	$190.04	$190.05	$190.00
Purchase #5	$115.58	4.203%	$120.4378	$120.44	$120.45	$120.40
Purchase #6	$156.93	9.779%	$172.2762	$172.28	$172.30	$172.30
Purchase #7	$76.60	11.573%	$85.4649	$85.46	$85.45	$85.50
7 purchase totals =	$876.49		$945.8686	$945.87	$945.85	$945.90