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	$63.59	12.873%	$71.7759	$71.78	$71.80	$71.80
Purchase #2	$161.65	3.724%	$167.6698	$167.67	$167.65	$167.70
Purchase #3	$90.41	10.171%	$99.6056	$99.61	$99.60	$99.60
Purchase #4	$132.80	5.200%	$139.7056	$139.71	$139.70	$139.70
Purchase #5	$225.84	6.111%	$239.6411	$239.64	$239.65	$239.60
Purchase #6	$106.34	10.553%	$117.5621	$117.56	$117.55	$117.60
Purchase #7	$194.64	13.677%	$221.2609	$221.26	$221.25	$221.30
7 purchase totals =	$975.27		$1,057.2210	$1,057.23	$1,057.20	$1,057.30