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	$126.30	13.521%	$143.377	$143.38	$143.40	$143.40
Purchase #2	$150.41	10.415%	$166.0752	$166.08	$166.10	$166.10
Purchase #3	$66.58	4.330%	$69.4629	$69.46	$69.45	$69.50
Purchase #4	$29.90	5.237%	$31.4659	$31.47	$31.45	$31.50
Purchase #5	$145.82	9.148%	$159.1596	$159.16	$159.15	$159.20
Purchase #6	$243.70	4.754%	$255.2855	$255.29	$255.30	$255.30
Purchase #7	$45.69	7.288%	$49.0199	$49.02	$49.00	$49.00
7 purchase totals =	$808.40		$873.8460	$873.86	$873.85	$874.00