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	$171.53	4.698%	$179.5885	$179.59	$179.60	$179.60
Purchase #2	$171.34	9.417%	$187.4751	$187.48	$187.50	$187.50
Purchase #3	$68.92	13.757%	$78.4013	$78.40	$78.40	$78.40
Purchase #4	$235.69	13.327%	$267.1004	$267.10	$267.10	$267.10
Purchase #5	$159.54	13.110%	$180.4557	$180.46	$180.45	$180.50
Purchase #6	$78.94	10.318%	$87.085	$87.09	$87.10	$87.10
Purchase #7	$88.30	13.802%	$100.4872	$100.49	$100.50	$100.50
7 purchase totals =	$974.26		$1,080.5932	$1,080.61	$1,080.65	$1,080.70