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	$140.50	7.149%	$150.5443	$150.54	$150.55	$150.50
Purchase #2	$108.30	6.697%	$115.5529	$115.55	$115.55	$115.60
Purchase #3	$61.29	10.529%	$67.7432	$67.74	$67.75	$67.70
Purchase #4	$38.39	12.398%	$43.1496	$43.15	$43.15	$43.10
Purchase #5	$110.48	11.348%	$123.0173	$123.02	$123.00	$123.00
Purchase #6	$226.35	12.777%	$255.2707	$255.27	$255.25	$255.30
Purchase #7	$234.29	12.171%	$262.8054	$262.81	$262.80	$262.80
7 purchase totals =	$919.60		$1,018.0834	$1,018.08	$1,018.05	$1,018.00