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	$165.89	11.664%	$185.2394	$185.24	$185.25	$185.20
Purchase #2	$101.84	9.586%	$111.6024	$111.60	$111.60	$111.60
Purchase #3	$197.98	11.816%	$221.3733	$221.37	$221.35	$221.40
Purchase #4	$65.38	6.847%	$69.8566	$69.86	$69.85	$69.90
Purchase #5	$161.58	12.534%	$181.8324	$181.83	$181.85	$181.80
Purchase #6	$24.36	5.460%	$25.6901	$25.69	$25.70	$25.70
Purchase #7	$59.66	11.593%	$66.5764	$66.58	$66.60	$66.60
7 purchase totals =	$776.69		$862.1706	$862.17	$862.20	$862.20