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	$98.75	6.580%	$105.2478	$105.25	$105.25	$105.20
Purchase #2	$233.25	11.203%	$259.381	$259.38	$259.40	$259.40
Purchase #3	$19.95	11.789%	$22.3019	$22.30	$22.30	$22.30
Purchase #4	$146.42	10.451%	$161.7224	$161.72	$161.70	$161.70
Purchase #5	$87.37	13.797%	$99.4244	$99.42	$99.40	$99.40
Purchase #6	$86.80	4.570%	$90.7668	$90.77	$90.75	$90.80
Purchase #7	$127.84	10.464%	$141.2172	$141.22	$141.20	$141.20
7 purchase totals =	$800.38		$880.0615	$880.06	$880.00	$880.00