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	$170.66	9.267%	$186.4751	$186.48	$186.50	$186.50
Purchase #2	$56.27	5.153%	$59.1696	$59.17	$59.15	$59.20
Purchase #3	$135.45	12.553%	$152.453	$152.45	$152.45	$152.50
Purchase #4	$47.44	5.697%	$50.1427	$50.14	$50.15	$50.10
Purchase #5	$165.47	4.469%	$172.8649	$172.86	$172.85	$172.90
Purchase #6	$124.70	7.402%	$133.9303	$133.93	$133.95	$133.90
Purchase #7	$101.82	8.604%	$110.5806	$110.58	$110.60	$110.60
7 purchase totals =	$801.81		$865.6162	$865.61	$865.65	$865.70