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	$22.72	6.220%	$24.1332	$24.13	$24.15	$24.10
Purchase #2	$87.63	3.328%	$90.5463	$90.55	$90.55	$90.50
Purchase #3	$171.93	4.612%	$179.8594	$179.86	$179.85	$179.90
Purchase #4	$45.36	13.326%	$51.4047	$51.40	$51.40	$51.40
Purchase #5	$106.47	10.313%	$117.4503	$117.45	$117.45	$117.50
Purchase #6	$145.95	10.282%	$160.9566	$160.96	$160.95	$161.00
Purchase #7	$152.46	7.784%	$164.3275	$164.33	$164.35	$164.30
7 purchase totals =	$732.52		$788.6780	$788.68	$788.70	$788.70