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	$12.46	5.871%	$13.1915	$13.19	$13.20	$13.20
Purchase #2	$100.55	4.689%	$105.2648	$105.26	$105.25	$105.30
Purchase #3	$134.95	7.177%	$144.6354	$144.64	$144.65	$144.60
Purchase #4	$102.38	6.622%	$109.1596	$109.16	$109.15	$109.20
Purchase #5	$27.43	12.614%	$30.89	$30.89	$30.90	$30.90
Purchase #6	$236.76	12.198%	$265.64	$265.64	$265.65	$265.60
Purchase #7	$128.67	7.583%	$138.427	$138.43	$138.45	$138.40
7 purchase totals =	$743.20		$807.2083	$807.21	$807.25	$807.20