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	$81.27	11.482%	$90.6014	$90.60	$90.60	$90.60
Purchase #2	$31.74	6.626%	$33.8431	$33.84	$33.85	$33.80
Purchase #3	$135.72	13.719%	$154.3394	$154.34	$154.35	$154.30
Purchase #4	$151.70	9.860%	$166.6576	$166.66	$166.65	$166.70
Purchase #5	$17.38	12.397%	$19.5346	$19.53	$19.55	$19.50
Purchase #6	$181.32	11.555%	$202.2715	$202.27	$202.25	$202.30
Purchase #7	$114.78	10.707%	$127.0695	$127.07	$127.05	$127.10
7 purchase totals =	$713.91		$794.3171	$794.31	$794.30	$794.30