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	$105.64	10.311%	$116.5325	$116.53	$116.55	$116.50
Purchase #2	$116.37	10.769%	$128.9019	$128.90	$128.90	$128.90
Purchase #3	$127.89	10.870%	$141.7916	$141.79	$141.80	$141.80
Purchase #4	$218.32	11.289%	$242.9661	$242.97	$242.95	$243.00
Purchase #5	$116.61	13.794%	$132.6952	$132.70	$132.70	$132.70
Purchase #6	$112.52	10.731%	$124.5945	$124.59	$124.60	$124.60
Purchase #7	$18.26	10.161%	$20.1154	$20.12	$20.10	$20.10
7 purchase totals =	$815.61		$907.5972	$907.60	$907.60	$907.60