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	$230.57	10.723%	$255.294	$255.29	$255.30	$255.30
Purchase #2	$83.82	3.229%	$86.5265	$86.53	$86.55	$86.50
Purchase #3	$20.31	9.566%	$22.2529	$22.25	$22.25	$22.30
Purchase #4	$161.34	7.113%	$172.8161	$172.82	$172.80	$172.80
Purchase #5	$207.98	12.327%	$233.6177	$233.62	$233.60	$233.60
Purchase #6	$21.40	6.427%	$22.7754	$22.78	$22.80	$22.80
Purchase #7	$160.42	3.245%	$165.6256	$165.63	$165.65	$165.60
7 purchase totals =	$885.84		$958.9082	$958.92	$958.95	$958.90