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	$5.41	9.244%	$5.9101	$5.91	$5.90	$5.90
Purchase #2	$128.53	13.201%	$145.4972	$145.50	$145.50	$145.50
Purchase #3	$166.31	10.307%	$183.4516	$183.45	$183.45	$183.50
Purchase #4	$152.40	6.387%	$162.1338	$162.13	$162.15	$162.10
Purchase #5	$77.58	10.188%	$85.4839	$85.48	$85.50	$85.50
Purchase #6	$24.27	3.274%	$25.0646	$25.06	$25.05	$25.10
Purchase #7	$106.70	6.756%	$113.9087	$113.91	$113.90	$113.90
7 purchase totals =	$661.20		$721.4499	$721.44	$721.45	$721.50