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	$178.65	3.743%	$185.3369	$185.34	$185.35	$185.30
Purchase #2	$191.64	13.523%	$217.5555	$217.56	$217.55	$217.60
Purchase #3	$34.35	11.412%	$38.27	$38.27	$38.25	$38.30
Purchase #4	$108.59	12.860%	$122.5547	$122.55	$122.55	$122.60
Purchase #5	$136.84	8.208%	$148.0718	$148.07	$148.05	$148.10
Purchase #6	$59.52	12.299%	$66.8404	$66.84	$66.85	$66.80
Purchase #7	$38.57	10.780%	$42.7278	$42.73	$42.75	$42.70
7 purchase totals =	$748.16		$821.3571	$821.36	$821.35	$821.40