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	$138.68	11.833%	$155.09	$155.09	$155.10	$155.10
Purchase #2	$85.37	7.807%	$92.0348	$92.03	$92.05	$92.00
Purchase #3	$145.69	8.809%	$158.5238	$158.52	$158.50	$158.50
Purchase #4	$159.70	13.244%	$180.8507	$180.85	$180.85	$180.90
Purchase #5	$44.43	5.644%	$46.9376	$46.94	$46.95	$46.90
Purchase #6	$59.86	12.482%	$67.3317	$67.33	$67.35	$67.30
Purchase #7	$73.81	13.608%	$83.8541	$83.85	$83.85	$83.90
7 purchase totals =	$707.54		$784.6227	$784.61	$784.65	$784.60