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	$12.59	10.308%	$13.8878	$13.89	$13.90	$13.90
Purchase #2	$165.82	8.143%	$179.3227	$179.32	$179.30	$179.30
Purchase #3	$159.25	12.362%	$178.9365	$178.94	$178.95	$178.90
Purchase #4	$222.53	8.328%	$241.0623	$241.06	$241.05	$241.10
Purchase #5	$173.79	13.309%	$196.9197	$196.92	$196.90	$196.90
Purchase #6	$249.69	6.619%	$266.217	$266.22	$266.20	$266.20
Purchase #7	$130.72	10.344%	$144.2417	$144.24	$144.25	$144.20
7 purchase totals =	$1,114.39		$1,220.5877	$1,220.59	$1,220.55	$1,220.50