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	$7.84	9.784%	$8.6071	$8.61	$8.60	$8.60
Purchase #2	$111.82	10.227%	$123.2558	$123.26	$123.25	$123.30
Purchase #3	$120.35	7.193%	$129.0068	$129.01	$129.00	$129.00
Purchase #4	$62.52	5.478%	$65.9448	$65.94	$65.95	$65.90
Purchase #5	$48.84	11.429%	$54.4219	$54.42	$54.40	$54.40
Purchase #6	$237.48	7.856%	$256.1364	$256.14	$256.15	$256.10
Purchase #7	$82.82	10.297%	$91.348	$91.35	$91.35	$91.30
7 purchase totals =	$671.67		$728.7208	$728.73	$728.70	$728.60