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	$126.44	8.661%	$137.391	$137.39	$137.40	$137.40
Purchase #2	$213.42	10.518%	$235.8675	$235.87	$235.85	$235.90
Purchase #3	$171.33	13.685%	$194.7765	$194.78	$194.80	$194.80
Purchase #4	$204.29	11.243%	$227.2583	$227.26	$227.25	$227.30
Purchase #5	$147.83	3.446%	$152.9242	$152.92	$152.90	$152.90
Purchase #6	$34.63	3.458%	$35.8275	$35.83	$35.85	$35.80
Purchase #7	$238.67	4.522%	$249.4627	$249.46	$249.45	$249.50
7 purchase totals =	$1,136.61		$1,233.5077	$1,233.51	$1,233.50	$1,233.60