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	$238.75	12.572%	$268.7657	$268.77	$268.75	$268.80
Purchase #2	$153.48	11.292%	$170.811	$170.81	$170.80	$170.80
Purchase #3	$11.94	13.307%	$13.5289	$13.53	$13.55	$13.50
Purchase #4	$41.59	6.816%	$44.4248	$44.42	$44.40	$44.40
Purchase #5	$139.79	3.654%	$144.8979	$144.90	$144.90	$144.90
Purchase #6	$100.51	10.595%	$111.159	$111.16	$111.15	$111.20
Purchase #7	$104.86	13.444%	$118.9574	$118.96	$118.95	$119.00
7 purchase totals =	$790.92		$872.5447	$872.55	$872.50	$872.60