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	$151.59	11.139%	$168.4756	$168.48	$168.50	$168.50
Purchase #2	$221.89	3.725%	$230.1554	$230.16	$230.15	$230.20
Purchase #3	$11.52	8.560%	$12.5061	$12.51	$12.50	$12.50
Purchase #4	$82.90	8.254%	$89.7426	$89.74	$89.75	$89.70
Purchase #5	$192.52	6.342%	$204.7296	$204.73	$204.75	$204.70
Purchase #6	$79.45	3.222%	$82.0099	$82.01	$82.00	$82.00
Purchase #7	$129.32	11.170%	$143.765	$143.77	$143.75	$143.80
7 purchase totals =	$869.19		$931.3842	$931.40	$931.40	$931.40