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	$71.50	12.481%	$80.4239	$80.42	$80.40	$80.40
Purchase #2	$16.96	5.115%	$17.8275	$17.83	$17.85	$17.80
Purchase #3	$236.96	8.269%	$256.5542	$256.55	$256.55	$256.60
Purchase #4	$163.66	7.770%	$176.3764	$176.38	$176.40	$176.40
Purchase #5	$99.39	12.598%	$111.9112	$111.91	$111.90	$111.90
Purchase #6	$55.74	6.301%	$59.2522	$59.25	$59.25	$59.30
Purchase #7	$92.56	13.635%	$105.1806	$105.18	$105.20	$105.20
7 purchase totals =	$736.77		$807.5260	$807.52	$807.55	$807.60