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	$102.82	5.270%	$108.2386	$108.24	$108.25	$108.20
Purchase #2	$131.41	9.620%	$144.0516	$144.05	$144.05	$144.10
Purchase #3	$139.42	12.746%	$157.1905	$157.19	$157.20	$157.20
Purchase #4	$144.41	5.462%	$152.2977	$152.30	$152.30	$152.30
Purchase #5	$78.58	13.620%	$89.2826	$89.28	$89.30	$89.30
Purchase #6	$250.39	13.286%	$283.6568	$283.66	$283.65	$283.70
Purchase #7	$81.94	10.734%	$90.7354	$90.74	$90.75	$90.70
7 purchase totals =	$928.97		$1,025.4532	$1,025.46	$1,025.50	$1,025.50