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	$22.79	7.485%	$24.4958	$24.50	$24.50	$24.50
Purchase #2	$123.82	12.717%	$139.5662	$139.57	$139.55	$139.60
Purchase #3	$208.90	5.816%	$221.0496	$221.05	$221.05	$221.00
Purchase #4	$198.74	12.468%	$223.5189	$223.52	$223.50	$223.50
Purchase #5	$158.29	13.357%	$179.4328	$179.43	$179.45	$179.40
Purchase #6	$145.25	6.687%	$154.9629	$154.96	$154.95	$155.00
Purchase #7	$29.30	13.776%	$33.3364	$33.34	$33.35	$33.30
7 purchase totals =	$887.09		$976.3626	$976.37	$976.35	$976.30