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	$147.92	12.387%	$166.2429	$166.24	$166.25	$166.20
Purchase #2	$242.75	13.228%	$274.861	$274.86	$274.85	$274.90
Purchase #3	$133.47	8.513%	$144.8323	$144.83	$144.85	$144.80
Purchase #4	$183.62	7.140%	$196.7305	$196.73	$196.75	$196.70
Purchase #5	$82.60	6.418%	$87.9013	$87.90	$87.90	$87.90
Purchase #6	$106.36	9.501%	$116.4653	$116.47	$116.45	$116.50
Purchase #7	$164.89	11.675%	$184.1409	$184.14	$184.15	$184.10
7 purchase totals =	$1,061.61		$1,171.1742	$1,171.17	$1,171.20	$1,171.10