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	$79.42	13.527%	$90.1631	$90.16	$90.15	$90.20
Purchase #2	$124.90	4.765%	$130.8515	$130.85	$130.85	$130.90
Purchase #3	$91.48	10.220%	$100.8293	$100.83	$100.85	$100.80
Purchase #4	$93.78	8.219%	$101.4878	$101.49	$101.50	$101.50
Purchase #5	$70.86	6.326%	$75.3426	$75.34	$75.35	$75.30
Purchase #6	$77.87	5.583%	$82.2175	$82.22	$82.20	$82.20
Purchase #7	$230.95	13.668%	$262.5162	$262.52	$262.50	$262.50
7 purchase totals =	$769.26		$843.4080	$843.41	$843.40	$843.40