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	$139.96	4.690%	$146.5241	$146.52	$146.50	$146.50
Purchase #2	$80.26	8.764%	$87.294	$87.29	$87.30	$87.30
Purchase #3	$233.92	9.440%	$256.002	$256.00	$256.00	$256.00
Purchase #4	$93.53	6.325%	$99.4458	$99.45	$99.45	$99.40
Purchase #5	$11.55	12.233%	$12.9629	$12.96	$12.95	$13.00
Purchase #6	$67.31	5.630%	$71.0996	$71.10	$71.10	$71.10
Purchase #7	$231.94	6.302%	$246.5569	$246.56	$246.55	$246.60
7 purchase totals =	$858.47		$919.8853	$919.88	$919.85	$919.90