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	$49.81	7.800%	$53.6952	$53.70	$53.70	$53.70
Purchase #2	$166.40	12.264%	$186.8073	$186.81	$186.80	$186.80
Purchase #3	$89.49	9.184%	$97.7088	$97.71	$97.70	$97.70
Purchase #4	$89.58	13.251%	$101.4502	$101.45	$101.45	$101.50
Purchase #5	$122.54	3.775%	$127.1659	$127.17	$127.15	$127.20
Purchase #6	$231.28	10.371%	$255.266	$255.27	$255.25	$255.30
Purchase #7	$103.90	8.211%	$112.4312	$112.43	$112.45	$112.40
7 purchase totals =	$853.00		$934.5246	$934.54	$934.50	$934.60