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	$86.88	3.708%	$90.1015	$90.10	$90.10	$90.10
Purchase #2	$101.99	12.219%	$114.4522	$114.45	$114.45	$114.50
Purchase #3	$228.27	6.549%	$243.2194	$243.22	$243.20	$243.20
Purchase #4	$118.92	7.261%	$127.5548	$127.55	$127.55	$127.60
Purchase #5	$113.52	7.328%	$121.8387	$121.84	$121.85	$121.80
Purchase #6	$82.33	12.237%	$92.4047	$92.40	$92.40	$92.40
Purchase #7	$101.30	4.219%	$105.5738	$105.57	$105.55	$105.60
7 purchase totals =	$833.21		$895.1451	$895.13	$895.10	$895.20