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	$54.52	4.249%	$56.8366	$56.84	$56.85	$56.80
Purchase #2	$64.64	9.558%	$70.8183	$70.82	$70.80	$70.80
Purchase #3	$40.38	4.680%	$42.2698	$42.27	$42.25	$42.30
Purchase #4	$172.54	5.433%	$181.9141	$181.91	$181.90	$181.90
Purchase #5	$84.62	11.501%	$94.3521	$94.35	$94.35	$94.40
Purchase #6	$191.81	12.478%	$215.7441	$215.74	$215.75	$215.70
Purchase #7	$179.96	5.687%	$190.1943	$190.19	$190.20	$190.20
7 purchase totals =	$788.47		$852.1293	$852.12	$852.10	$852.10