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	$133.52	6.228%	$141.8356	$141.84	$141.85	$141.80
Purchase #2	$118.41	4.525%	$123.7681	$123.77	$123.75	$123.80
Purchase #3	$228.48	13.196%	$258.6302	$258.63	$258.65	$258.60
Purchase #4	$140.36	8.379%	$152.1208	$152.12	$152.10	$152.10
Purchase #5	$92.43	8.571%	$100.3522	$100.35	$100.35	$100.40
Purchase #6	$41.43	4.830%	$43.4311	$43.43	$43.45	$43.40
Purchase #7	$19.87	6.328%	$21.1274	$21.13	$21.15	$21.10
7 purchase totals =	$774.50		$841.2654	$841.27	$841.30	$841.20