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	$64.48	4.353%	$67.2868	$67.29	$67.30	$67.30
Purchase #2	$135.43	7.640%	$145.7769	$145.78	$145.80	$145.80
Purchase #3	$107.74	11.340%	$119.9577	$119.96	$119.95	$120.00
Purchase #4	$21.74	8.181%	$23.5185	$23.52	$23.50	$23.50
Purchase #5	$58.81	13.275%	$66.617	$66.62	$66.60	$66.60
Purchase #6	$115.74	6.572%	$123.3464	$123.35	$123.35	$123.30
Purchase #7	$80.78	10.305%	$89.1044	$89.10	$89.10	$89.10
7 purchase totals =	$584.72		$635.6077	$635.62	$635.60	$635.60