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	$123.77	4.109%	$128.8557	$128.86	$128.85	$128.90
Purchase #2	$31.45	7.458%	$33.7955	$33.80	$33.80	$33.80
Purchase #3	$87.29	3.387%	$90.2465	$90.25	$90.25	$90.20
Purchase #4	$103.67	5.406%	$109.2744	$109.27	$109.25	$109.30
Purchase #5	$45.88	11.488%	$51.1507	$51.15	$51.15	$51.20
Purchase #6	$197.42	6.187%	$209.6344	$209.63	$209.65	$209.60
Purchase #7	$81.33	13.487%	$92.299	$92.30	$92.30	$92.30
7 purchase totals =	$670.81		$715.2562	$715.26	$715.25	$715.30