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	$192.47	13.540%	$218.5304	$218.53	$218.55	$218.50
Purchase #2	$221.39	5.420%	$233.3893	$233.39	$233.40	$233.40
Purchase #3	$82.80	9.666%	$90.8034	$90.80	$90.80	$90.80
Purchase #4	$211.98	13.358%	$240.2963	$240.30	$240.30	$240.30
Purchase #5	$239.42	10.489%	$264.5328	$264.53	$264.55	$264.50
Purchase #6	$225.74	7.201%	$241.9955	$242.00	$242.00	$242.00
Purchase #7	$207.40	11.149%	$230.523	$230.52	$230.50	$230.50
7 purchase totals =	$1,381.20		$1,520.0707	$1,520.07	$1,520.10	$1,520.00