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	$82.33	10.197%	$90.7252	$90.73	$90.75	$90.70
Purchase #2	$135.57	6.189%	$143.9604	$143.96	$143.95	$144.00
Purchase #3	$52.52	13.625%	$59.6759	$59.68	$59.70	$59.70
Purchase #4	$54.60	12.210%	$61.2667	$61.27	$61.25	$61.30
Purchase #5	$112.71	11.739%	$125.941	$125.94	$125.95	$125.90
Purchase #6	$61.28	3.175%	$63.2256	$63.23	$63.25	$63.20
Purchase #7	$214.92	12.865%	$242.5695	$242.57	$242.55	$242.60
7 purchase totals =	$713.93		$787.3643	$787.38	$787.40	$787.40