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	$90.71	13.550%	$103.0012	$103.00	$103.00	$103.00
Purchase #2	$238.61	5.663%	$252.1225	$252.12	$252.10	$252.10
Purchase #3	$225.58	13.771%	$256.6446	$256.64	$256.65	$256.60
Purchase #4	$36.78	9.751%	$40.3664	$40.37	$40.35	$40.40
Purchase #5	$51.62	7.802%	$55.6474	$55.65	$55.65	$55.60
Purchase #6	$55.55	8.845%	$60.4634	$60.46	$60.45	$60.50
Purchase #7	$49.44	8.172%	$53.4802	$53.48	$53.50	$53.50
7 purchase totals =	$748.29		$821.7257	$821.72	$821.70	$821.70