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	$18.51	12.590%	$20.8404	$20.84	$20.85	$20.80
Purchase #2	$156.37	6.714%	$166.8687	$166.87	$166.85	$166.90
Purchase #3	$162.44	6.259%	$172.6071	$172.61	$172.60	$172.60
Purchase #4	$239.36	13.626%	$271.9752	$271.98	$272.00	$272.00
Purchase #5	$222.62	10.696%	$246.4314	$246.43	$246.45	$246.40
Purchase #6	$181.70	3.622%	$188.2812	$188.28	$188.30	$188.30
Purchase #7	$101.27	8.497%	$109.8749	$109.87	$109.85	$109.90
7 purchase totals =	$1,082.27		$1,176.8789	$1,176.88	$1,176.90	$1,176.90