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	$249.98	8.512%	$271.2583	$271.26	$271.25	$271.30
Purchase #2	$111.96	4.155%	$116.6119	$116.61	$116.60	$116.60
Purchase #3	$170.48	4.287%	$177.7885	$177.79	$177.80	$177.80
Purchase #4	$49.25	11.851%	$55.0866	$55.09	$55.10	$55.10
Purchase #5	$103.33	12.744%	$116.4984	$116.50	$116.50	$116.50
Purchase #6	$192.39	11.502%	$214.5187	$214.52	$214.50	$214.50
Purchase #7	$187.59	4.863%	$196.7125	$196.71	$196.70	$196.70
7 purchase totals =	$1,064.98		$1,148.4749	$1,148.48	$1,148.45	$1,148.50