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	$79.69	7.341%	$85.54	$85.54	$85.55	$85.50
Purchase #2	$241.31	10.473%	$266.5824	$266.58	$266.60	$266.60
Purchase #3	$148.47	5.644%	$156.8496	$156.85	$156.85	$156.80
Purchase #4	$87.50	3.607%	$90.6561	$90.66	$90.65	$90.70
Purchase #5	$27.78	7.104%	$29.7535	$29.75	$29.75	$29.80
Purchase #6	$221.30	9.419%	$242.1442	$242.14	$242.15	$242.10
Purchase #7	$164.49	13.661%	$186.961	$186.96	$186.95	$187.00
7 purchase totals =	$970.54		$1,058.4868	$1,058.48	$1,058.50	$1,058.50