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	$168.66	10.254%	$185.9544	$185.95	$185.95	$186.00
Purchase #2	$58.82	13.814%	$66.9454	$66.95	$66.95	$66.90
Purchase #3	$227.48	10.149%	$250.5669	$250.57	$250.55	$250.60
Purchase #4	$228.32	8.845%	$248.5149	$248.51	$248.50	$248.50
Purchase #5	$55.86	4.661%	$58.4636	$58.46	$58.45	$58.50
Purchase #6	$55.61	8.670%	$60.4314	$60.43	$60.45	$60.40
Purchase #7	$26.78	6.850%	$28.6144	$28.61	$28.60	$28.60
7 purchase totals =	$821.53		$899.4910	$899.48	$899.45	$899.50