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	$155.78	8.174%	$168.5135	$168.51	$168.50	$168.50
Purchase #2	$29.63	11.377%	$33.001	$33.00	$33.00	$33.00
Purchase #3	$48.51	3.249%	$50.0861	$50.09	$50.10	$50.10
Purchase #4	$43.90	12.544%	$49.4068	$49.41	$49.40	$49.40
Purchase #5	$128.93	12.746%	$145.3634	$145.36	$145.35	$145.40
Purchase #6	$7.31	10.791%	$8.0988	$8.10	$8.10	$8.10
Purchase #7	$144.72	5.757%	$153.0515	$153.05	$153.05	$153.10
7 purchase totals =	$558.78		$607.5211	$607.52	$607.50	$607.60