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	$38.78	13.125%	$43.8699	$43.87	$43.85	$43.90
Purchase #2	$135.55	10.338%	$149.5632	$149.56	$149.55	$149.60
Purchase #3	$42.92	9.277%	$46.9017	$46.90	$46.90	$46.90
Purchase #4	$190.66	11.467%	$212.523	$212.52	$212.50	$212.50
Purchase #5	$165.63	4.810%	$173.5968	$173.60	$173.60	$173.60
Purchase #6	$40.29	6.269%	$42.8158	$42.82	$42.80	$42.80
Purchase #7	$88.96	10.505%	$98.3052	$98.31	$98.30	$98.30
7 purchase totals =	$702.79		$767.5756	$767.58	$767.50	$767.60