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	$18.52	12.565%	$20.847	$20.85	$20.85	$20.80
Purchase #2	$40.55	13.286%	$45.9375	$45.94	$45.95	$45.90
Purchase #3	$6.66	5.449%	$7.0229	$7.02	$7.00	$7.00
Purchase #4	$167.85	10.724%	$185.8502	$185.85	$185.85	$185.90
Purchase #5	$105.78	13.127%	$119.6657	$119.67	$119.65	$119.70
Purchase #6	$230.42	4.165%	$240.017	$240.02	$240.00	$240.00
Purchase #7	$63.54	10.208%	$70.0262	$70.03	$70.05	$70.00
7 purchase totals =	$633.32		$689.3665	$689.38	$689.35	$689.30