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	$170.64	13.370%	$193.4546	$193.45	$193.45	$193.50
Purchase #2	$148.64	5.147%	$156.2905	$156.29	$156.30	$156.30
Purchase #3	$62.25	4.653%	$65.1465	$65.15	$65.15	$65.10
Purchase #4	$127.62	9.164%	$139.3151	$139.32	$139.30	$139.30
Purchase #5	$146.72	13.566%	$166.624	$166.62	$166.60	$166.60
Purchase #6	$35.58	11.764%	$39.7656	$39.77	$39.75	$39.80
Purchase #7	$99.46	6.427%	$105.8523	$105.85	$105.85	$105.90
7 purchase totals =	$790.91		$866.4486	$866.45	$866.40	$866.50