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	$156.90	6.642%	$167.3213	$167.32	$167.30	$167.30
Purchase #2	$34.63	13.407%	$39.2728	$39.27	$39.25	$39.30
Purchase #3	$232.64	3.243%	$240.1845	$240.18	$240.20	$240.20
Purchase #4	$38.56	11.135%	$42.8537	$42.85	$42.85	$42.90
Purchase #5	$54.54	7.580%	$58.6741	$58.67	$58.65	$58.70
Purchase #6	$131.49	9.528%	$144.0184	$144.02	$144.00	$144.00
Purchase #7	$16.38	13.342%	$18.5654	$18.57	$18.55	$18.60
7 purchase totals =	$665.14		$710.8902	$710.88	$710.80	$711.00