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	$199.43	12.262%	$223.8841	$223.88	$223.90	$223.90
Purchase #2	$5.28	10.188%	$5.8179	$5.82	$5.80	$5.80
Purchase #3	$80.60	12.185%	$90.4211	$90.42	$90.40	$90.40
Purchase #4	$248.54	9.151%	$271.2839	$271.28	$271.30	$271.30
Purchase #5	$153.45	7.382%	$164.7777	$164.78	$164.80	$164.80
Purchase #6	$88.37	12.862%	$99.7361	$99.74	$99.75	$99.70
Purchase #7	$102.49	8.265%	$110.9608	$110.96	$110.95	$111.00
7 purchase totals =	$878.16		$966.8816	$966.88	$966.90	$966.90