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	$215.36	11.769%	$240.7057	$240.71	$240.70	$240.70
Purchase #2	$79.46	12.227%	$89.1756	$89.18	$89.20	$89.20
Purchase #3	$182.46	5.552%	$192.5902	$192.59	$192.60	$192.60
Purchase #4	$93.41	9.324%	$102.1195	$102.12	$102.10	$102.10
Purchase #5	$48.35	7.476%	$51.9646	$51.96	$51.95	$52.00
Purchase #6	$41.88	4.552%	$43.7864	$43.79	$43.80	$43.80
Purchase #7	$20.59	4.260%	$21.4671	$21.47	$21.45	$21.50
7 purchase totals =	$681.51		$741.8091	$741.82	$741.80	$741.90