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	$234.38	9.860%	$257.4899	$257.49	$257.50	$257.50
Purchase #2	$158.35	4.714%	$165.8146	$165.81	$165.80	$165.80
Purchase #3	$184.62	5.520%	$194.811	$194.81	$194.80	$194.80
Purchase #4	$33.98	11.737%	$37.9682	$37.97	$37.95	$38.00
Purchase #5	$93.50	10.500%	$103.3175	$103.32	$103.30	$103.30
Purchase #6	$46.94	5.508%	$49.5255	$49.53	$49.55	$49.50
Purchase #7	$182.37	7.698%	$196.4088	$196.41	$196.40	$196.40
7 purchase totals =	$934.14		$1,005.3355	$1,005.34	$1,005.30	$1,005.30