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	$133.78	10.790%	$148.2149	$148.21	$148.20	$148.20
Purchase #2	$35.45	11.808%	$39.6359	$39.64	$39.65	$39.60
Purchase #3	$146.93	13.521%	$166.7964	$166.80	$166.80	$166.80
Purchase #4	$132.77	5.658%	$140.2821	$140.28	$140.30	$140.30
Purchase #5	$179.70	9.228%	$196.2827	$196.28	$196.30	$196.30
Purchase #6	$53.25	10.842%	$59.0234	$59.02	$59.00	$59.00
Purchase #7	$166.74	10.119%	$183.6124	$183.61	$183.60	$183.60
7 purchase totals =	$848.62		$933.8478	$933.84	$933.85	$933.80