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	$146.49	8.199%	$158.5007	$158.50	$158.50	$158.50
Purchase #2	$84.52	11.495%	$94.2356	$94.24	$94.25	$94.20
Purchase #3	$63.95	13.176%	$72.3761	$72.38	$72.40	$72.40
Purchase #4	$193.41	10.777%	$214.2538	$214.25	$214.25	$214.30
Purchase #5	$202.33	10.771%	$224.123	$224.12	$224.10	$224.10
Purchase #6	$102.88	6.223%	$109.2822	$109.28	$109.30	$109.30
Purchase #7	$77.25	7.163%	$82.7834	$82.78	$82.80	$82.80
7 purchase totals =	$870.83		$955.5548	$955.55	$955.60	$955.60