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	$47.64	13.599%	$54.1186	$54.12	$54.10	$54.10
Purchase #2	$134.58	11.213%	$149.6705	$149.67	$149.65	$149.70
Purchase #3	$115.72	3.172%	$119.3906	$119.39	$119.40	$119.40
Purchase #4	$34.97	5.333%	$36.835	$36.84	$36.85	$36.80
Purchase #5	$113.56	12.662%	$127.939	$127.94	$127.95	$127.90
Purchase #6	$116.41	6.510%	$123.9883	$123.99	$124.00	$124.00
Purchase #7	$156.78	7.499%	$168.5369	$168.54	$168.55	$168.50
7 purchase totals =	$719.66		$780.4789	$780.49	$780.50	$780.40