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	$40.72	3.791%	$42.2637	$42.26	$42.25	$42.30
Purchase #2	$155.59	7.655%	$167.5004	$167.50	$167.50	$167.50
Purchase #3	$37.32	10.742%	$41.3289	$41.33	$41.35	$41.30
Purchase #4	$113.38	8.630%	$123.1647	$123.16	$123.15	$123.20
Purchase #5	$177.96	3.440%	$184.0818	$184.08	$184.10	$184.10
Purchase #6	$208.89	13.478%	$237.0442	$237.04	$237.05	$237.00
Purchase #7	$143.31	5.553%	$151.268	$151.27	$151.25	$151.30
7 purchase totals =	$877.17		$946.6517	$946.64	$946.65	$946.70