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	$20.63	5.539%	$21.7727	$21.77	$21.75	$21.80
Purchase #2	$131.37	11.769%	$146.8309	$146.83	$146.85	$146.80
Purchase #3	$209.99	13.339%	$238.0006	$238.00	$238.00	$238.00
Purchase #4	$54.54	6.629%	$58.1555	$58.16	$58.15	$58.20
Purchase #5	$163.51	13.227%	$185.1375	$185.14	$185.15	$185.10
Purchase #6	$185.81	7.175%	$199.1419	$199.14	$199.15	$199.10
Purchase #7	$111.94	10.544%	$123.743	$123.74	$123.75	$123.70
7 purchase totals =	$877.79		$972.7821	$972.78	$972.80	$972.70