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	$66.87	6.654%	$71.3195	$71.32	$71.30	$71.30
Purchase #2	$114.42	11.652%	$127.7522	$127.75	$127.75	$127.80
Purchase #3	$233.27	3.227%	$240.7976	$240.80	$240.80	$240.80
Purchase #4	$18.89	6.571%	$20.1313	$20.13	$20.15	$20.10
Purchase #5	$93.28	8.426%	$101.1398	$101.14	$101.15	$101.10
Purchase #6	$185.96	10.784%	$206.0139	$206.01	$206.00	$206.00
Purchase #7	$199.54	13.506%	$226.4899	$226.49	$226.50	$226.50
7 purchase totals =	$912.23		$993.6442	$993.64	$993.65	$993.60