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	$82.82	8.575%	$89.9218	$89.92	$89.90	$89.90
Purchase #2	$81.68	4.674%	$85.4977	$85.50	$85.50	$85.50
Purchase #3	$114.43	10.471%	$126.412	$126.41	$126.40	$126.40
Purchase #4	$26.43	5.308%	$27.8329	$27.83	$27.85	$27.80
Purchase #5	$145.98	7.449%	$156.8541	$156.85	$156.85	$156.90
Purchase #6	$32.70	8.496%	$35.4782	$35.48	$35.50	$35.50
Purchase #7	$87.31	7.841%	$94.156	$94.16	$94.15	$94.20
7 purchase totals =	$571.35		$616.1527	$616.15	$616.15	$616.20