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	$249.84	5.433%	$263.4138	$263.41	$263.40	$263.40
Purchase #2	$107.88	3.313%	$111.4541	$111.45	$111.45	$111.50
Purchase #3	$119.29	13.397%	$135.2713	$135.27	$135.25	$135.30
Purchase #4	$176.36	3.476%	$182.4903	$182.49	$182.50	$182.50
Purchase #5	$162.59	8.517%	$176.4378	$176.44	$176.45	$176.40
Purchase #6	$17.58	6.824%	$18.7797	$18.78	$18.80	$18.80
Purchase #7	$163.80	6.245%	$174.0293	$174.03	$174.05	$174.00
7 purchase totals =	$997.34		$1,061.8763	$1,061.87	$1,061.90	$1,061.90