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	$63.28	4.666%	$66.2326	$66.23	$66.25	$66.20
Purchase #2	$47.78	12.226%	$53.6216	$53.62	$53.60	$53.60
Purchase #3	$93.45	13.201%	$105.7863	$105.79	$105.80	$105.80
Purchase #4	$112.38	4.116%	$117.0056	$117.01	$117.00	$117.00
Purchase #5	$35.59	11.637%	$39.7316	$39.73	$39.75	$39.70
Purchase #6	$74.78	7.546%	$80.4229	$80.42	$80.40	$80.40
Purchase #7	$85.74	12.657%	$96.5921	$96.59	$96.60	$96.60
7 purchase totals =	$513.00		$559.3927	$559.39	$559.40	$559.30