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	$27.27	8.358%	$29.5492	$29.55	$29.55	$29.50
Purchase #2	$64.85	9.269%	$70.8609	$70.86	$70.85	$70.90
Purchase #3	$166.72	11.306%	$185.5694	$185.57	$185.55	$185.60
Purchase #4	$184.51	5.277%	$194.2466	$194.25	$194.25	$194.20
Purchase #5	$214.93	10.220%	$236.8958	$236.90	$236.90	$236.90
Purchase #6	$174.90	6.120%	$185.6039	$185.60	$185.60	$185.60
Purchase #7	$90.46	12.505%	$101.772	$101.77	$101.75	$101.80
7 purchase totals =	$923.64		$1,004.4978	$1,004.50	$1,004.45	$1,004.50