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	$6.79	10.491%	$7.5023	$7.50	$7.50	$7.50
Purchase #2	$166.64	13.695%	$189.4613	$189.46	$189.45	$189.50
Purchase #3	$206.68	8.603%	$224.4607	$224.46	$224.45	$224.50
Purchase #4	$152.38	8.816%	$165.8138	$165.81	$165.80	$165.80
Purchase #5	$61.78	3.707%	$64.0702	$64.07	$64.05	$64.10
Purchase #6	$198.89	13.546%	$225.8316	$225.83	$225.85	$225.80
Purchase #7	$146.66	6.790%	$156.6182	$156.62	$156.60	$156.60
7 purchase totals =	$939.82		$1,033.7581	$1,033.75	$1,033.70	$1,033.80