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	$35.83	10.487%	$39.5875	$39.59	$39.60	$39.60
Purchase #2	$172.74	7.464%	$185.6333	$185.63	$185.65	$185.60
Purchase #3	$14.50	5.524%	$15.301	$15.30	$15.30	$15.30
Purchase #4	$151.41	3.219%	$156.2839	$156.28	$156.30	$156.30
Purchase #5	$83.37	9.668%	$91.4302	$91.43	$91.45	$91.40
Purchase #6	$159.40	8.607%	$173.1196	$173.12	$173.10	$173.10
Purchase #7	$136.42	7.648%	$146.8534	$146.85	$146.85	$146.90
7 purchase totals =	$753.67		$808.2089	$808.20	$808.25	$808.20