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	$40.69	11.768%	$45.4784	$45.48	$45.50	$45.50
Purchase #2	$107.79	6.227%	$114.5021	$114.50	$114.50	$114.50
Purchase #3	$129.43	11.597%	$144.44	$144.44	$144.45	$144.40
Purchase #4	$33.50	11.621%	$37.393	$37.39	$37.40	$37.40
Purchase #5	$143.42	3.640%	$148.6405	$148.64	$148.65	$148.60
Purchase #6	$24.52	9.667%	$26.8903	$26.89	$26.90	$26.90
Purchase #7	$19.80	8.274%	$21.4383	$21.44	$21.45	$21.40
7 purchase totals =	$499.15		$538.7826	$538.78	$538.85	$538.70