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	$128.29	10.650%	$141.9529	$141.95	$141.95	$142.00
Purchase #2	$217.34	9.743%	$238.5154	$238.52	$238.50	$238.50
Purchase #3	$207.85	6.233%	$220.8053	$220.81	$220.80	$220.80
Purchase #4	$127.93	11.601%	$142.7712	$142.77	$142.75	$142.80
Purchase #5	$52.60	6.335%	$55.9322	$55.93	$55.95	$55.90
Purchase #6	$69.93	9.417%	$76.5153	$76.52	$76.50	$76.50
Purchase #7	$246.58	13.450%	$279.745	$279.75	$279.75	$279.70
7 purchase totals =	$1,050.52		$1,156.2373	$1,156.25	$1,156.20	$1,156.20