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	$25.52	12.152%	$28.6212	$28.62	$28.60	$28.60
Purchase #2	$188.57	5.819%	$199.5429	$199.54	$199.55	$199.50
Purchase #3	$58.30	12.375%	$65.5146	$65.51	$65.50	$65.50
Purchase #4	$99.97	12.608%	$112.5742	$112.57	$112.55	$112.60
Purchase #5	$77.47	7.396%	$83.1997	$83.20	$83.20	$83.20
Purchase #6	$172.37	9.526%	$188.79	$188.79	$188.80	$188.80
Purchase #7	$113.39	4.552%	$118.5515	$118.55	$118.55	$118.60
7 purchase totals =	$735.59		$796.7941	$796.78	$796.75	$796.80