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	$143.37	11.872%	$160.3909	$160.39	$160.40	$160.40
Purchase #2	$41.54	4.721%	$43.5011	$43.50	$43.50	$43.50
Purchase #3	$148.40	6.300%	$157.7492	$157.75	$157.75	$157.70
Purchase #4	$79.42	13.517%	$90.1552	$90.16	$90.15	$90.20
Purchase #5	$21.74	11.191%	$24.1729	$24.17	$24.15	$24.20
Purchase #6	$165.73	13.839%	$188.6654	$188.67	$188.65	$188.70
Purchase #7	$106.84	3.785%	$110.8839	$110.88	$110.90	$110.90
7 purchase totals =	$707.04		$775.5186	$775.52	$775.50	$775.60