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	$56.77	6.239%	$60.3119	$60.31	$60.30	$60.30
Purchase #2	$197.83	12.359%	$222.2798	$222.28	$222.30	$222.30
Purchase #3	$88.80	12.508%	$99.9071	$99.91	$99.90	$99.90
Purchase #4	$129.85	7.692%	$139.8381	$139.84	$139.85	$139.80
Purchase #5	$162.88	9.698%	$178.6761	$178.68	$178.70	$178.70
Purchase #6	$250.75	13.495%	$284.5887	$284.59	$284.60	$284.60
Purchase #7	$18.91	7.140%	$20.2602	$20.26	$20.25	$20.30
7 purchase totals =	$905.79		$1,005.8619	$1,005.87	$1,005.90	$1,005.90