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	$69.97	11.598%	$78.0851	$78.09	$78.10	$78.10
Purchase #2	$205.60	11.813%	$229.8875	$229.89	$229.90	$229.90
Purchase #3	$238.65	11.274%	$265.5554	$265.56	$265.55	$265.60
Purchase #4	$146.36	8.286%	$158.4874	$158.49	$158.50	$158.50
Purchase #5	$218.83	13.605%	$248.6018	$248.60	$248.60	$248.60
Purchase #6	$18.89	7.303%	$20.2695	$20.27	$20.25	$20.30
Purchase #7	$249.78	5.604%	$263.7777	$263.78	$263.80	$263.80
7 purchase totals =	$1,148.08		$1,264.6644	$1,264.68	$1,264.70	$1,264.80