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	$192.88	9.126%	$210.4822	$210.48	$210.50	$210.50
Purchase #2	$185.59	12.244%	$208.3136	$208.31	$208.30	$208.30
Purchase #3	$124.52	12.287%	$139.8198	$139.82	$139.80	$139.80
Purchase #4	$117.38	9.293%	$128.2881	$128.29	$128.30	$128.30
Purchase #5	$27.27	8.211%	$29.5091	$29.51	$29.50	$29.50
Purchase #6	$65.78	8.510%	$71.3779	$71.38	$71.40	$71.40
Purchase #7	$124.53	13.389%	$141.2033	$141.20	$141.20	$141.20
7 purchase totals =	$837.95		$928.9940	$928.99	$929.00	$929.00