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	$85.91	6.514%	$91.5062	$91.51	$91.50	$91.50
Purchase #2	$20.69	13.672%	$23.5187	$23.52	$23.50	$23.50
Purchase #3	$48.29	7.371%	$51.8495	$51.85	$51.85	$51.80
Purchase #4	$172.72	12.843%	$194.9024	$194.90	$194.90	$194.90
Purchase #5	$166.29	11.683%	$185.7177	$185.72	$185.70	$185.70
Purchase #6	$78.95	8.871%	$85.9537	$85.95	$85.95	$86.00
Purchase #7	$66.51	10.847%	$73.7243	$73.72	$73.70	$73.70
7 purchase totals =	$639.36		$707.1725	$707.17	$707.10	$707.10