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	$91.99	9.619%	$100.8385	$100.84	$100.85	$100.80
Purchase #2	$123.47	10.140%	$135.9899	$135.99	$136.00	$136.00
Purchase #3	$160.34	5.367%	$168.9454	$168.95	$168.95	$168.90
Purchase #4	$116.81	5.493%	$123.2264	$123.23	$123.25	$123.20
Purchase #5	$17.46	6.433%	$18.5832	$18.58	$18.60	$18.60
Purchase #6	$67.90	12.701%	$76.524	$76.52	$76.50	$76.50
Purchase #7	$195.42	11.800%	$218.4796	$218.48	$218.50	$218.50
7 purchase totals =	$773.39		$842.5870	$842.59	$842.65	$842.50