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	$229.87	4.151%	$239.4119	$239.41	$239.40	$239.40
Purchase #2	$166.45	7.809%	$179.4481	$179.45	$179.45	$179.40
Purchase #3	$111.98	10.164%	$123.3616	$123.36	$123.35	$123.40
Purchase #4	$96.25	4.290%	$100.3791	$100.38	$100.40	$100.40
Purchase #5	$146.73	3.157%	$151.3623	$151.36	$151.35	$151.40
Purchase #6	$74.76	4.167%	$77.8752	$77.88	$77.90	$77.90
Purchase #7	$12.70	5.389%	$13.3844	$13.38	$13.40	$13.40
7 purchase totals =	$838.74		$885.2226	$885.22	$885.25	$885.30