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	$60.63	3.187%	$62.5623	$62.56	$62.55	$62.60
Purchase #2	$78.53	9.731%	$86.1718	$86.17	$86.15	$86.20
Purchase #3	$231.89	11.757%	$259.1533	$259.15	$259.15	$259.20
Purchase #4	$135.98	5.548%	$143.5242	$143.52	$143.50	$143.50
Purchase #5	$83.54	10.323%	$92.1638	$92.16	$92.15	$92.20
Purchase #6	$34.95	9.790%	$38.3716	$38.37	$38.35	$38.40
Purchase #7	$85.71	13.674%	$97.43	$97.43	$97.45	$97.40
7 purchase totals =	$711.23		$779.3770	$779.36	$779.30	$779.50