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	$236.41	5.365%	$249.0934	$249.09	$249.10	$249.10
Purchase #2	$136.46	11.109%	$151.6193	$151.62	$151.60	$151.60
Purchase #3	$245.87	13.372%	$278.7477	$278.75	$278.75	$278.70
Purchase #4	$33.57	11.380%	$37.3903	$37.39	$37.40	$37.40
Purchase #5	$198.85	7.818%	$214.3961	$214.40	$214.40	$214.40
Purchase #6	$18.87	12.658%	$21.2586	$21.26	$21.25	$21.30
Purchase #7	$64.53	4.675%	$67.5468	$67.55	$67.55	$67.50
7 purchase totals =	$934.56		$1,020.0522	$1,020.06	$1,020.05	$1,020.00