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	$214.89	13.270%	$243.4059	$243.41	$243.40	$243.40
Purchase #2	$160.54	6.472%	$170.9301	$170.93	$170.95	$170.90
Purchase #3	$104.77	12.238%	$117.5918	$117.59	$117.60	$117.60
Purchase #4	$231.90	9.184%	$253.1977	$253.20	$253.20	$253.20
Purchase #5	$113.49	8.195%	$122.7905	$122.79	$122.80	$122.80
Purchase #6	$37.62	11.245%	$41.8504	$41.85	$41.85	$41.90
Purchase #7	$54.73	8.792%	$59.5419	$59.54	$59.55	$59.50
7 purchase totals =	$917.94		$1,009.3083	$1,009.31	$1,009.35	$1,009.30