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	$19.30	5.761%	$20.4119	$20.41	$20.40	$20.40
Purchase #2	$125.44	13.449%	$142.3104	$142.31	$142.30	$142.30
Purchase #3	$44.58	7.381%	$47.8704	$47.87	$47.85	$47.90
Purchase #4	$210.80	3.810%	$218.8315	$218.83	$218.85	$218.80
Purchase #5	$242.84	13.255%	$275.0284	$275.03	$275.05	$275.00
Purchase #6	$134.72	7.795%	$145.2214	$145.22	$145.20	$145.20
Purchase #7	$199.50	11.578%	$222.5981	$222.60	$222.60	$222.60
7 purchase totals =	$977.18		$1,072.2721	$1,072.27	$1,072.25	$1,072.20