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	$7.61	8.789%	$8.2788	$8.28	$8.30	$8.30
Purchase #2	$103.49	7.499%	$111.2507	$111.25	$111.25	$111.30
Purchase #3	$98.69	4.440%	$103.0718	$103.07	$103.05	$103.10
Purchase #4	$216.54	6.686%	$231.0179	$231.02	$231.00	$231.00
Purchase #5	$165.36	4.381%	$172.6044	$172.60	$172.60	$172.60
Purchase #6	$180.96	5.313%	$190.5744	$190.57	$190.55	$190.60
Purchase #7	$214.66	8.792%	$233.5329	$233.53	$233.55	$233.50
7 purchase totals =	$987.31		$1,050.3309	$1,050.32	$1,050.30	$1,050.40