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	$47.46	6.607%	$50.5957	$50.60	$50.60	$50.60
Purchase #2	$75.43	8.154%	$81.5806	$81.58	$81.60	$81.60
Purchase #3	$145.25	9.736%	$159.3915	$159.39	$159.40	$159.40
Purchase #4	$164.51	10.350%	$181.5368	$181.54	$181.55	$181.50
Purchase #5	$89.29	7.440%	$95.9332	$95.93	$95.95	$95.90
Purchase #6	$165.50	6.847%	$176.8318	$176.83	$176.85	$176.80
Purchase #7	$53.25	12.110%	$59.6986	$59.70	$59.70	$59.70
7 purchase totals =	$740.69		$805.5682	$805.57	$805.65	$805.50