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	$149.74	4.588%	$156.6101	$156.61	$156.60	$156.60
Purchase #2	$197.54	5.726%	$208.8511	$208.85	$208.85	$208.90
Purchase #3	$192.99	11.556%	$215.2919	$215.29	$215.30	$215.30
Purchase #4	$70.33	9.375%	$76.9234	$76.92	$76.90	$76.90
Purchase #5	$154.67	4.680%	$161.9086	$161.91	$161.90	$161.90
Purchase #6	$92.91	8.128%	$100.4617	$100.46	$100.45	$100.50
Purchase #7	$111.27	7.311%	$119.4049	$119.40	$119.40	$119.40
7 purchase totals =	$969.45		$1,039.4517	$1,039.44	$1,039.40	$1,039.50