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	$205.68	8.716%	$223.6071	$223.61	$223.60	$223.60
Purchase #2	$81.25	10.260%	$89.5863	$89.59	$89.60	$89.60
Purchase #3	$11.39	11.809%	$12.735	$12.74	$12.75	$12.70
Purchase #4	$14.72	5.537%	$15.535	$15.54	$15.55	$15.50
Purchase #5	$173.86	5.316%	$183.1024	$183.10	$183.10	$183.10
Purchase #6	$66.85	9.579%	$73.2536	$73.25	$73.25	$73.30
Purchase #7	$184.95	3.760%	$191.9041	$191.90	$191.90	$191.90
7 purchase totals =	$738.70		$789.7235	$789.73	$789.75	$789.70