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	$126.42	12.129%	$141.7535	$141.75	$141.75	$141.80
Purchase #2	$21.39	7.824%	$23.0636	$23.06	$23.05	$23.10
Purchase #3	$157.53	5.768%	$166.6163	$166.62	$166.60	$166.60
Purchase #4	$89.50	10.748%	$99.1195	$99.12	$99.10	$99.10
Purchase #5	$130.80	11.512%	$145.8577	$145.86	$145.85	$145.90
Purchase #6	$140.83	10.261%	$155.2806	$155.28	$155.30	$155.30
Purchase #7	$94.31	12.567%	$106.1619	$106.16	$106.15	$106.20
7 purchase totals =	$760.78		$837.8531	$837.85	$837.80	$838.00