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	$10.89	9.300%	$11.9028	$11.90	$11.90	$11.90
Purchase #2	$82.50	8.641%	$89.6288	$89.63	$89.65	$89.60
Purchase #3	$76.42	7.540%	$82.1821	$82.18	$82.20	$82.20
Purchase #4	$105.64	6.204%	$112.1939	$112.19	$112.20	$112.20
Purchase #5	$148.46	4.186%	$154.6745	$154.67	$154.65	$154.70
Purchase #6	$109.55	13.161%	$123.9679	$123.97	$123.95	$124.00
Purchase #7	$249.97	7.427%	$268.5353	$268.54	$268.55	$268.50
7 purchase totals =	$783.43		$843.0853	$843.08	$843.10	$843.10