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	$237.73	7.358%	$255.2222	$255.22	$255.20	$255.20
Purchase #2	$60.58	11.320%	$67.4377	$67.44	$67.45	$67.40
Purchase #3	$176.25	10.549%	$194.8426	$194.84	$194.85	$194.80
Purchase #4	$160.28	8.784%	$174.359	$174.36	$174.35	$174.40
Purchase #5	$151.62	11.160%	$168.5408	$168.54	$168.55	$168.50
Purchase #6	$32.43	6.300%	$34.4731	$34.47	$34.45	$34.50
Purchase #7	$159.26	7.506%	$171.2141	$171.21	$171.20	$171.20
7 purchase totals =	$978.15		$1,066.0895	$1,066.08	$1,066.05	$1,066.00