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	$119.65	7.405%	$128.5101	$128.51	$128.50	$128.50
Purchase #2	$136.42	5.189%	$143.4988	$143.50	$143.50	$143.50
Purchase #3	$122.38	5.281%	$128.8429	$128.84	$128.85	$128.80
Purchase #4	$208.44	9.292%	$227.8082	$227.81	$227.80	$227.80
Purchase #5	$113.49	12.723%	$127.9293	$127.93	$127.95	$127.90
Purchase #6	$81.46	8.445%	$88.3393	$88.34	$88.35	$88.30
Purchase #7	$78.89	8.291%	$85.4308	$85.43	$85.45	$85.40
7 purchase totals =	$860.73		$930.3594	$930.36	$930.40	$930.20