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	$72.63	13.634%	$82.5324	$82.53	$82.55	$82.50
Purchase #2	$82.90	7.583%	$89.1863	$89.19	$89.20	$89.20
Purchase #3	$185.93	3.743%	$192.8894	$192.89	$192.90	$192.90
Purchase #4	$231.28	4.286%	$241.1927	$241.19	$241.20	$241.20
Purchase #5	$152.92	11.708%	$170.8239	$170.82	$170.80	$170.80
Purchase #6	$250.66	3.259%	$258.829	$258.83	$258.85	$258.80
Purchase #7	$126.77	13.620%	$144.0361	$144.04	$144.05	$144.00
7 purchase totals =	$1,103.09		$1,179.4898	$1,179.49	$1,179.55	$1,179.40