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	$71.59	6.835%	$76.4832	$76.48	$76.50	$76.50
Purchase #2	$229.58	3.682%	$238.0331	$238.03	$238.05	$238.00
Purchase #3	$218.52	3.182%	$225.4733	$225.47	$225.45	$225.50
Purchase #4	$37.85	9.850%	$41.5782	$41.58	$41.60	$41.60
Purchase #5	$186.76	7.494%	$200.7558	$200.76	$200.75	$200.80
Purchase #6	$111.50	13.648%	$126.7175	$126.72	$126.70	$126.70
Purchase #7	$142.89	13.156%	$161.6886	$161.69	$161.70	$161.70
7 purchase totals =	$998.69		$1,070.7297	$1,070.73	$1,070.75	$1,070.80