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	$41.41	8.613%	$44.9766	$44.98	$45.00	$45.00
Purchase #2	$137.43	13.314%	$155.7274	$155.73	$155.75	$155.70
Purchase #3	$66.94	12.667%	$75.4193	$75.42	$75.40	$75.40
Purchase #4	$221.51	12.160%	$248.4456	$248.45	$248.45	$248.40
Purchase #5	$116.99	12.433%	$131.5354	$131.54	$131.55	$131.50
Purchase #6	$36.87	10.723%	$40.8236	$40.82	$40.80	$40.80
Purchase #7	$52.46	9.583%	$57.4872	$57.49	$57.50	$57.50
7 purchase totals =	$673.61		$754.4151	$754.43	$754.45	$754.30