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	$52.74	9.858%	$57.9391	$57.94	$57.95	$57.90
Purchase #2	$53.42	3.671%	$55.381	$55.38	$55.40	$55.40
Purchase #3	$166.30	12.312%	$186.7749	$186.77	$186.75	$186.80
Purchase #4	$139.83	11.333%	$155.6769	$155.68	$155.70	$155.70
Purchase #5	$87.37	3.335%	$90.2838	$90.28	$90.30	$90.30
Purchase #6	$7.27	6.383%	$7.734	$7.73	$7.75	$7.70
Purchase #7	$63.36	13.542%	$71.9402	$71.94	$71.95	$71.90
7 purchase totals =	$570.29		$625.7299	$625.72	$625.80	$625.70