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	$145.29	3.492%	$150.3635	$150.36	$150.35	$150.40
Purchase #2	$105.99	3.189%	$109.37	$109.37	$109.35	$109.40
Purchase #3	$198.73	13.687%	$225.9302	$225.93	$225.95	$225.90
Purchase #4	$73.88	11.724%	$82.5417	$82.54	$82.55	$82.50
Purchase #5	$36.73	11.192%	$40.8408	$40.84	$40.85	$40.80
Purchase #6	$137.90	9.395%	$150.8557	$150.86	$150.85	$150.90
Purchase #7	$193.56	3.234%	$199.8197	$199.82	$199.80	$199.80
7 purchase totals =	$892.08		$959.7216	$959.72	$959.70	$959.70