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	$102.37	10.790%	$113.4157	$113.42	$113.40	$113.40
Purchase #2	$16.93	8.449%	$18.3604	$18.36	$18.35	$18.40
Purchase #3	$95.61	9.380%	$104.5782	$104.58	$104.60	$104.60
Purchase #4	$116.58	10.302%	$128.5901	$128.59	$128.60	$128.60
Purchase #5	$140.48	10.633%	$155.4172	$155.42	$155.40	$155.40
Purchase #6	$237.27	5.140%	$249.4657	$249.47	$249.45	$249.50
Purchase #7	$47.48	12.849%	$53.5807	$53.58	$53.60	$53.60
7 purchase totals =	$756.72		$823.4080	$823.42	$823.40	$823.50