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	$130.52	13.687%	$148.3843	$148.38	$148.40	$148.40
Purchase #2	$72.49	6.229%	$77.0054	$77.01	$77.00	$77.00
Purchase #3	$35.38	11.610%	$39.4876	$39.49	$39.50	$39.50
Purchase #4	$163.52	5.412%	$172.3697	$172.37	$172.35	$172.40
Purchase #5	$93.26	13.433%	$105.7876	$105.79	$105.80	$105.80
Purchase #6	$170.63	9.871%	$187.4729	$187.47	$187.45	$187.50
Purchase #7	$95.85	13.308%	$108.6057	$108.61	$108.60	$108.60
7 purchase totals =	$761.65		$839.1132	$839.12	$839.10	$839.20