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	$50.62	11.502%	$56.4423	$56.44	$56.45	$56.40
Purchase #2	$20.32	13.689%	$23.1016	$23.10	$23.10	$23.10
Purchase #3	$117.54	11.836%	$131.452	$131.45	$131.45	$131.50
Purchase #4	$141.54	8.277%	$153.2553	$153.26	$153.25	$153.30
Purchase #5	$62.87	12.299%	$70.6024	$70.60	$70.60	$70.60
Purchase #6	$99.68	5.511%	$105.1734	$105.17	$105.15	$105.20
Purchase #7	$97.32	4.348%	$101.5515	$101.55	$101.55	$101.60
7 purchase totals =	$589.89		$641.5785	$641.57	$641.55	$641.70