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	$9.70	12.488%	$10.9113	$10.91	$10.90	$10.90
Purchase #2	$177.54	7.186%	$190.298	$190.30	$190.30	$190.30
Purchase #3	$121.25	9.152%	$132.3468	$132.35	$132.35	$132.30
Purchase #4	$240.78	7.183%	$258.0752	$258.08	$258.10	$258.10
Purchase #5	$90.87	9.123%	$99.1601	$99.16	$99.15	$99.20
Purchase #6	$105.57	11.700%	$117.9217	$117.92	$117.90	$117.90
Purchase #7	$143.75	9.172%	$156.9348	$156.93	$156.95	$156.90
7 purchase totals =	$889.46		$965.6479	$965.65	$965.65	$965.60