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	$153.58	11.731%	$171.5965	$171.60	$171.60	$171.60
Purchase #2	$132.86	9.422%	$145.3781	$145.38	$145.40	$145.40
Purchase #3	$159.72	5.499%	$168.503	$168.50	$168.50	$168.50
Purchase #4	$54.71	12.483%	$61.5394	$61.54	$61.55	$61.50
Purchase #5	$196.54	11.273%	$218.696	$218.70	$218.70	$218.70
Purchase #6	$25.52	8.847%	$27.7778	$27.78	$27.80	$27.80
Purchase #7	$232.57	13.392%	$263.7158	$263.72	$263.70	$263.70
7 purchase totals =	$955.50		$1,057.2066	$1,057.22	$1,057.25	$1,057.20