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	$13.88	13.378%	$15.7369	$15.74	$15.75	$15.70
Purchase #2	$100.42	5.178%	$105.6197	$105.62	$105.60	$105.60
Purchase #3	$54.86	3.113%	$56.5678	$56.57	$56.55	$56.60
Purchase #4	$197.36	13.568%	$224.1378	$224.14	$224.15	$224.10
Purchase #5	$47.95	10.299%	$52.8884	$52.89	$52.90	$52.90
Purchase #6	$209.58	11.142%	$232.9314	$232.93	$232.95	$232.90
Purchase #7	$85.26	5.693%	$90.1139	$90.11	$90.10	$90.10
7 purchase totals =	$709.31		$777.9959	$778.00	$778.00	$777.90