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	$59.69	11.127%	$66.3317	$66.33	$66.35	$66.30
Purchase #2	$146.69	5.215%	$154.3399	$154.34	$154.35	$154.30
Purchase #3	$123.63	3.787%	$128.3119	$128.31	$128.30	$128.30
Purchase #4	$231.87	8.484%	$251.5419	$251.54	$251.55	$251.50
Purchase #5	$124.25	6.488%	$132.3113	$132.31	$132.30	$132.30
Purchase #6	$118.96	8.276%	$128.8051	$128.81	$128.80	$128.80
Purchase #7	$209.54	8.581%	$227.5206	$227.52	$227.50	$227.50
7 purchase totals =	$1,014.63		$1,089.1624	$1,089.16	$1,089.15	$1,089.00