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	$48.56	11.507%	$54.1478	$54.15	$54.15	$54.10
Purchase #2	$91.43	8.541%	$99.239	$99.24	$99.25	$99.20
Purchase #3	$242.96	9.519%	$266.0874	$266.09	$266.10	$266.10
Purchase #4	$29.32	6.594%	$31.2534	$31.25	$31.25	$31.30
Purchase #5	$55.64	12.205%	$62.4309	$62.43	$62.45	$62.40
Purchase #6	$147.32	12.298%	$165.4374	$165.44	$165.45	$165.40
Purchase #7	$248.49	5.250%	$261.5357	$261.54	$261.55	$261.50
7 purchase totals =	$863.72		$940.1316	$940.14	$940.20	$940.00