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	$184.25	12.776%	$207.7898	$207.79	$207.80	$207.80
Purchase #2	$36.79	3.848%	$38.2057	$38.21	$38.20	$38.20
Purchase #3	$204.28	11.624%	$228.0255	$228.03	$228.05	$228.00
Purchase #4	$177.40	10.697%	$196.3765	$196.38	$196.40	$196.40
Purchase #5	$231.46	8.163%	$250.3541	$250.35	$250.35	$250.40
Purchase #6	$60.69	11.674%	$67.775	$67.78	$67.80	$67.80
Purchase #7	$59.38	12.465%	$66.7817	$66.78	$66.80	$66.80
7 purchase totals =	$954.25		$1,055.3083	$1,055.32	$1,055.40	$1,055.40