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	$32.51	8.642%	$35.3195	$35.32	$35.30	$35.30
Purchase #2	$218.61	13.251%	$247.578	$247.58	$247.60	$247.60
Purchase #3	$89.81	6.734%	$95.8578	$95.86	$95.85	$95.90
Purchase #4	$9.56	11.364%	$10.6464	$10.65	$10.65	$10.60
Purchase #5	$221.65	7.650%	$238.6062	$238.61	$238.60	$238.60
Purchase #6	$124.29	5.539%	$131.1744	$131.17	$131.15	$131.20
Purchase #7	$219.50	6.450%	$233.6578	$233.66	$233.65	$233.70
7 purchase totals =	$915.93		$992.8401	$992.85	$992.80	$992.90