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	$190.48	12.726%	$214.7205	$214.72	$214.70	$214.70
Purchase #2	$82.84	9.649%	$90.8332	$90.83	$90.85	$90.80
Purchase #3	$226.32	8.599%	$245.7813	$245.78	$245.80	$245.80
Purchase #4	$28.80	4.719%	$30.1591	$30.16	$30.15	$30.20
Purchase #5	$159.56	10.192%	$175.8224	$175.82	$175.80	$175.80
Purchase #6	$60.66	9.275%	$66.2862	$66.29	$66.30	$66.30
Purchase #7	$50.42	7.697%	$54.3008	$54.30	$54.30	$54.30
7 purchase totals =	$799.08		$877.9035	$877.90	$877.90	$877.90