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	$165.29	13.502%	$187.6075	$187.61	$187.60	$187.60
Purchase #2	$18.30	9.735%	$20.0815	$20.08	$20.10	$20.10
Purchase #3	$59.77	13.606%	$67.9023	$67.90	$67.90	$67.90
Purchase #4	$231.65	10.242%	$255.3756	$255.38	$255.40	$255.40
Purchase #5	$90.86	13.496%	$103.1225	$103.12	$103.10	$103.10
Purchase #6	$138.89	3.187%	$143.3164	$143.32	$143.30	$143.30
Purchase #7	$32.48	11.659%	$36.2668	$36.27	$36.25	$36.30
7 purchase totals =	$737.24		$813.6726	$813.68	$813.65	$813.70