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	$211.32	6.651%	$225.3749	$225.37	$225.35	$225.40
Purchase #2	$114.36	11.418%	$127.4176	$127.42	$127.40	$127.40
Purchase #3	$35.75	12.669%	$40.2792	$40.28	$40.30	$40.30
Purchase #4	$162.84	12.647%	$183.4344	$183.43	$183.45	$183.40
Purchase #5	$234.43	12.295%	$263.2532	$263.25	$263.25	$263.30
Purchase #6	$148.86	11.515%	$166.0012	$166.00	$166.00	$166.00
Purchase #7	$226.43	10.155%	$249.424	$249.42	$249.40	$249.40
7 purchase totals =	$1,133.99		$1,255.1845	$1,255.17	$1,255.15	$1,255.20