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	$52.54	6.182%	$55.788	$55.79	$55.80	$55.80
Purchase #2	$87.94	6.395%	$93.5638	$93.56	$93.55	$93.60
Purchase #3	$230.94	10.536%	$255.2718	$255.27	$255.25	$255.30
Purchase #4	$131.71	10.392%	$145.3973	$145.40	$145.40	$145.40
Purchase #5	$64.99	9.796%	$71.3564	$71.36	$71.35	$71.40
Purchase #6	$6.73	10.739%	$7.4527	$7.45	$7.45	$7.50
Purchase #7	$75.93	12.760%	$85.6187	$85.62	$85.60	$85.60
7 purchase totals =	$650.78		$714.4487	$714.45	$714.40	$714.60