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	$141.93	9.152%	$154.9194	$154.92	$154.90	$154.90
Purchase #2	$176.90	7.714%	$190.5461	$190.55	$190.55	$190.50
Purchase #3	$219.69	12.462%	$247.0678	$247.07	$247.05	$247.10
Purchase #4	$12.35	9.742%	$13.5531	$13.55	$13.55	$13.60
Purchase #5	$19.32	4.807%	$20.2487	$20.25	$20.25	$20.20
Purchase #6	$166.97	11.749%	$186.5873	$186.59	$186.60	$186.60
Purchase #7	$31.63	5.766%	$33.4538	$33.45	$33.45	$33.50
7 purchase totals =	$768.79		$846.3762	$846.38	$846.35	$846.40