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	$80.69	5.677%	$85.2708	$85.27	$85.25	$85.30
Purchase #2	$110.38	11.677%	$123.2691	$123.27	$123.25	$123.30
Purchase #3	$131.39	11.757%	$146.8375	$146.84	$146.85	$146.80
Purchase #4	$244.49	4.561%	$255.6412	$255.64	$255.65	$255.60
Purchase #5	$25.46	10.619%	$28.1636	$28.16	$28.15	$28.20
Purchase #6	$49.73	8.294%	$53.8546	$53.85	$53.85	$53.90
Purchase #7	$31.87	7.375%	$34.2204	$34.22	$34.20	$34.20
7 purchase totals =	$674.01		$727.2572	$727.25	$727.20	$727.30