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	$24.57	3.810%	$25.5061	$25.51	$25.50	$25.50
Purchase #2	$51.40	6.132%	$54.5518	$54.55	$54.55	$54.60
Purchase #3	$242.98	13.296%	$275.2866	$275.29	$275.30	$275.30
Purchase #4	$120.50	6.304%	$128.0963	$128.10	$128.10	$128.10
Purchase #5	$84.89	6.461%	$90.3747	$90.37	$90.35	$90.40
Purchase #6	$144.99	11.187%	$161.21	$161.21	$161.20	$161.20
Purchase #7	$144.58	6.836%	$154.4635	$154.46	$154.45	$154.50
7 purchase totals =	$813.91		$889.4890	$889.49	$889.45	$889.60