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	$191.81	13.754%	$218.1915	$218.19	$218.20	$218.20
Purchase #2	$232.34	9.462%	$254.324	$254.32	$254.30	$254.30
Purchase #3	$55.92	13.166%	$63.2824	$63.28	$63.30	$63.30
Purchase #4	$86.60	4.627%	$90.607	$90.61	$90.60	$90.60
Purchase #5	$109.83	11.536%	$122.5	$122.50	$122.50	$122.50
Purchase #6	$223.36	4.386%	$233.1566	$233.16	$233.15	$233.20
Purchase #7	$177.59	5.773%	$187.8423	$187.84	$187.85	$187.80
7 purchase totals =	$1,077.45		$1,169.9038	$1,169.90	$1,169.90	$1,169.90