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	$135.71	3.771%	$140.8276	$140.83	$140.85	$140.80
Purchase #2	$216.95	10.759%	$240.2917	$240.29	$240.30	$240.30
Purchase #3	$178.64	5.325%	$188.1526	$188.15	$188.15	$188.20
Purchase #4	$26.30	8.627%	$28.5689	$28.57	$28.55	$28.60
Purchase #5	$85.41	4.703%	$89.4268	$89.43	$89.45	$89.40
Purchase #6	$210.40	13.364%	$238.5179	$238.52	$238.50	$238.50
Purchase #7	$87.25	3.730%	$90.5044	$90.50	$90.50	$90.50
7 purchase totals =	$940.66		$1,016.2899	$1,016.29	$1,016.30	$1,016.30