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	$78.38	6.636%	$83.5813	$83.58	$83.60	$83.60
Purchase #2	$240.90	11.396%	$268.353	$268.35	$268.35	$268.40
Purchase #3	$40.29	7.106%	$43.153	$43.15	$43.15	$43.20
Purchase #4	$74.82	4.481%	$78.1727	$78.17	$78.15	$78.20
Purchase #5	$220.39	4.518%	$230.3472	$230.35	$230.35	$230.30
Purchase #6	$6.42	11.540%	$7.1609	$7.16	$7.15	$7.20
Purchase #7	$54.49	7.540%	$58.5985	$58.60	$58.60	$58.60
7 purchase totals =	$715.69		$769.3666	$769.36	$769.35	$769.50