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	$166.59	7.605%	$179.2592	$179.26	$179.25	$179.30
Purchase #2	$183.78	8.216%	$198.8794	$198.88	$198.90	$198.90
Purchase #3	$55.91	3.337%	$57.7757	$57.78	$57.80	$57.80
Purchase #4	$167.68	10.388%	$185.0986	$185.10	$185.10	$185.10
Purchase #5	$15.33	13.626%	$17.4189	$17.42	$17.40	$17.40
Purchase #6	$117.25	11.609%	$130.8616	$130.86	$130.85	$130.90
Purchase #7	$104.79	6.730%	$111.8424	$111.84	$111.85	$111.80
7 purchase totals =	$811.33		$881.1358	$881.14	$881.15	$881.20