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	$19.34	11.402%	$21.5451	$21.55	$21.55	$21.50
Purchase #2	$62.48	4.261%	$65.1423	$65.14	$65.15	$65.10
Purchase #3	$150.56	10.613%	$166.5389	$166.54	$166.55	$166.50
Purchase #4	$132.42	13.281%	$150.0067	$150.01	$150.00	$150.00
Purchase #5	$209.64	11.731%	$234.2329	$234.23	$234.25	$234.20
Purchase #6	$157.81	10.488%	$174.3611	$174.36	$174.35	$174.40
Purchase #7	$134.58	10.114%	$148.1914	$148.19	$148.20	$148.20
7 purchase totals =	$866.83		$960.0184	$960.02	$960.05	$959.90