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	$103.66	6.447%	$110.343	$110.34	$110.35	$110.30
Purchase #2	$190.47	12.411%	$214.1092	$214.11	$214.10	$214.10
Purchase #3	$156.36	9.103%	$170.5935	$170.59	$170.60	$170.60
Purchase #4	$68.48	9.231%	$74.8014	$74.80	$74.80	$74.80
Purchase #5	$18.66	13.361%	$21.1532	$21.15	$21.15	$21.20
Purchase #6	$53.50	10.491%	$59.1127	$59.11	$59.10	$59.10
Purchase #7	$53.70	10.593%	$59.3884	$59.39	$59.40	$59.40
7 purchase totals =	$644.83		$709.5014	$709.49	$709.50	$709.50