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	$103.37	5.640%	$109.2001	$109.20	$109.20	$109.20
Purchase #2	$54.52	9.166%	$59.5173	$59.52	$59.50	$59.50
Purchase #3	$74.91	9.603%	$82.1036	$82.10	$82.10	$82.10
Purchase #4	$209.47	10.616%	$231.7073	$231.71	$231.70	$231.70
Purchase #5	$133.71	4.152%	$139.2616	$139.26	$139.25	$139.30
Purchase #6	$136.52	13.547%	$155.0144	$155.01	$155.00	$155.00
Purchase #7	$16.72	5.105%	$17.5736	$17.57	$17.55	$17.60
7 purchase totals =	$729.22		$794.3779	$794.37	$794.30	$794.40