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	$247.76	12.418%	$278.5268	$278.53	$278.55	$278.50
Purchase #2	$152.30	10.609%	$168.4575	$168.46	$168.45	$168.50
Purchase #3	$250.69	6.273%	$266.4158	$266.42	$266.40	$266.40
Purchase #4	$174.93	7.676%	$188.3576	$188.36	$188.35	$188.40
Purchase #5	$117.96	8.384%	$127.8498	$127.85	$127.85	$127.80
Purchase #6	$94.30	7.546%	$101.4159	$101.42	$101.40	$101.40
Purchase #7	$173.58	4.476%	$181.3494	$181.35	$181.35	$181.30
7 purchase totals =	$1,211.52		$1,312.3728	$1,312.39	$1,312.35	$1,312.30