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	$44.58	13.439%	$50.5711	$50.57	$50.55	$50.60
Purchase #2	$51.25	6.443%	$54.552	$54.55	$54.55	$54.60
Purchase #3	$176.64	8.141%	$191.0203	$191.02	$191.00	$191.00
Purchase #4	$6.68	13.145%	$7.5581	$7.56	$7.55	$7.60
Purchase #5	$126.34	5.486%	$133.271	$133.27	$133.25	$133.30
Purchase #6	$162.50	6.739%	$173.4509	$173.45	$173.45	$173.50
Purchase #7	$62.86	13.628%	$71.4266	$71.43	$71.45	$71.40
7 purchase totals =	$630.85		$681.8500	$681.85	$681.80	$682.00