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	$29.55	9.716%	$32.4211	$32.42	$32.40	$32.40
Purchase #2	$103.72	4.617%	$108.5088	$108.51	$108.50	$108.50
Purchase #3	$234.25	13.102%	$264.9414	$264.94	$264.95	$264.90
Purchase #4	$186.65	13.761%	$212.3349	$212.33	$212.35	$212.30
Purchase #5	$151.32	12.671%	$170.4938	$170.49	$170.50	$170.50
Purchase #6	$223.95	4.277%	$233.5283	$233.53	$233.55	$233.50
Purchase #7	$56.51	8.594%	$61.3665	$61.37	$61.35	$61.40
7 purchase totals =	$985.95		$1,083.5948	$1,083.59	$1,083.60	$1,083.50