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	$25.49	12.873%	$28.7713	$28.77	$28.75	$28.80
Purchase #2	$180.42	11.265%	$200.7443	$200.74	$200.75	$200.70
Purchase #3	$186.49	11.686%	$208.2832	$208.28	$208.30	$208.30
Purchase #4	$247.52	11.106%	$275.0096	$275.01	$275.00	$275.00
Purchase #5	$20.99	11.549%	$23.4141	$23.41	$23.40	$23.40
Purchase #6	$104.67	6.270%	$111.2328	$111.23	$111.25	$111.20
Purchase #7	$243.33	8.339%	$263.6213	$263.62	$263.60	$263.60
7 purchase totals =	$1,008.91		$1,111.0766	$1,111.06	$1,111.05	$1,111.00