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	$37.74	13.357%	$42.7809	$42.78	$42.80	$42.80
Purchase #2	$41.31	10.228%	$45.5352	$45.54	$45.55	$45.50
Purchase #3	$123.27	8.761%	$134.0697	$134.07	$134.05	$134.10
Purchase #4	$169.66	5.713%	$179.3527	$179.35	$179.35	$179.40
Purchase #5	$15.30	9.682%	$16.7813	$16.78	$16.80	$16.80
Purchase #6	$133.27	4.643%	$139.4577	$139.46	$139.45	$139.50
Purchase #7	$148.91	8.525%	$161.6046	$161.60	$161.60	$161.60
7 purchase totals =	$669.46		$719.5821	$719.58	$719.60	$719.70