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	$101.47	8.551%	$110.1467	$110.15	$110.15	$110.10
Purchase #2	$139.51	8.537%	$151.42	$151.42	$151.40	$151.40
Purchase #3	$82.86	11.756%	$92.601	$92.60	$92.60	$92.60
Purchase #4	$167.71	11.230%	$186.5438	$186.54	$186.55	$186.50
Purchase #5	$85.28	3.828%	$88.5445	$88.54	$88.55	$88.50
Purchase #6	$241.72	13.268%	$273.7914	$273.79	$273.80	$273.80
Purchase #7	$6.51	12.653%	$7.3337	$7.33	$7.35	$7.30
7 purchase totals =	$825.06		$910.3811	$910.37	$910.40	$910.20