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	$68.53	13.343%	$77.674	$77.67	$77.65	$77.70
Purchase #2	$109.88	12.266%	$123.3579	$123.36	$123.35	$123.40
Purchase #3	$66.99	8.209%	$72.4892	$72.49	$72.50	$72.50
Purchase #4	$177.31	4.604%	$185.4734	$185.47	$185.45	$185.50
Purchase #5	$54.49	9.662%	$59.7548	$59.75	$59.75	$59.80
Purchase #6	$14.35	8.500%	$15.5698	$15.57	$15.55	$15.60
Purchase #7	$53.61	10.712%	$59.3527	$59.35	$59.35	$59.40
7 purchase totals =	$545.16		$593.6718	$593.66	$593.60	$593.90