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	$12.25	6.312%	$13.0232	$13.02	$13.00	$13.00
Purchase #2	$197.40	9.303%	$215.7641	$215.76	$215.75	$215.80
Purchase #3	$56.31	5.215%	$59.2466	$59.25	$59.25	$59.20
Purchase #4	$51.37	8.805%	$55.8931	$55.89	$55.90	$55.90
Purchase #5	$208.76	5.838%	$220.9474	$220.95	$220.95	$220.90
Purchase #6	$89.72	13.141%	$101.5101	$101.51	$101.50	$101.50
Purchase #7	$66.98	4.566%	$70.0383	$70.04	$70.05	$70.00
7 purchase totals =	$682.79		$736.4228	$736.42	$736.40	$736.30