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	$59.51	12.215%	$66.7791	$66.78	$66.80	$66.80
Purchase #2	$172.81	13.819%	$196.6906	$196.69	$196.70	$196.70
Purchase #3	$114.56	12.764%	$129.1824	$129.18	$129.20	$129.20
Purchase #4	$231.83	12.249%	$260.2269	$260.23	$260.25	$260.20
Purchase #5	$133.98	4.301%	$139.7425	$139.74	$139.75	$139.70
Purchase #6	$42.59	13.339%	$48.2711	$48.27	$48.25	$48.30
Purchase #7	$46.75	9.124%	$51.0155	$51.02	$51.00	$51.00
7 purchase totals =	$802.03		$891.9081	$891.91	$891.95	$891.90