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	$147.30	12.335%	$165.4695	$165.47	$165.45	$165.50
Purchase #2	$236.40	5.711%	$249.9008	$249.90	$249.90	$249.90
Purchase #3	$120.86	13.424%	$137.0842	$137.08	$137.10	$137.10
Purchase #4	$146.39	7.425%	$157.2595	$157.26	$157.25	$157.30
Purchase #5	$223.78	8.672%	$243.1862	$243.19	$243.20	$243.20
Purchase #6	$80.49	11.772%	$89.9653	$89.97	$89.95	$90.00
Purchase #7	$227.61	12.268%	$255.5332	$255.53	$255.55	$255.50
7 purchase totals =	$1,182.83		$1,298.3987	$1,298.40	$1,298.40	$1,298.50