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	$19.64	9.478%	$21.5015	$21.50	$21.50	$21.50
Purchase #2	$227.31	5.123%	$238.9551	$238.96	$238.95	$239.00
Purchase #3	$162.43	5.449%	$171.2808	$171.28	$171.30	$171.30
Purchase #4	$230.69	10.680%	$255.3277	$255.33	$255.35	$255.30
Purchase #5	$53.30	10.275%	$58.7766	$58.78	$58.80	$58.80
Purchase #6	$39.84	8.832%	$43.3587	$43.36	$43.35	$43.40
Purchase #7	$231.33	4.186%	$241.0135	$241.01	$241.00	$241.00
7 purchase totals =	$964.54		$1,030.2139	$1,030.22	$1,030.25	$1,030.30