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	$250.53	9.256%	$273.7191	$273.72	$273.70	$273.70
Purchase #2	$27.39	6.834%	$29.2618	$29.26	$29.25	$29.30
Purchase #3	$95.53	4.487%	$99.8164	$99.82	$99.80	$99.80
Purchase #4	$50.51	8.633%	$54.8705	$54.87	$54.85	$54.90
Purchase #5	$38.64	8.862%	$42.0643	$42.06	$42.05	$42.10
Purchase #6	$167.96	7.193%	$180.0414	$180.04	$180.05	$180.00
Purchase #7	$212.51	7.734%	$228.9455	$228.95	$228.95	$228.90
7 purchase totals =	$843.07		$908.7190	$908.72	$908.65	$908.70