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	$140.79	12.602%	$158.5324	$158.53	$158.55	$158.50
Purchase #2	$205.61	12.756%	$231.8376	$231.84	$231.85	$231.80
Purchase #3	$79.72	11.859%	$89.174	$89.17	$89.15	$89.20
Purchase #4	$178.30	12.533%	$200.6463	$200.65	$200.65	$200.60
Purchase #5	$54.83	6.683%	$58.4943	$58.49	$58.50	$58.50
Purchase #6	$144.99	3.818%	$150.5257	$150.53	$150.55	$150.50
Purchase #7	$26.70	9.385%	$29.2058	$29.21	$29.20	$29.20
7 purchase totals =	$830.94		$918.4161	$918.42	$918.45	$918.30