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	$240.77	9.376%	$263.3446	$263.34	$263.35	$263.30
Purchase #2	$151.29	9.667%	$165.9152	$165.92	$165.90	$165.90
Purchase #3	$26.77	4.870%	$28.0737	$28.07	$28.05	$28.10
Purchase #4	$120.98	8.722%	$131.5319	$131.53	$131.55	$131.50
Purchase #5	$172.86	8.411%	$187.3993	$187.40	$187.40	$187.40
Purchase #6	$25.77	5.110%	$27.0868	$27.09	$27.10	$27.10
Purchase #7	$38.81	11.450%	$43.2537	$43.25	$43.25	$43.30
7 purchase totals =	$777.25		$846.6052	$846.60	$846.60	$846.60