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	$61.66	6.737%	$65.814	$65.81	$65.80	$65.80
Purchase #2	$215.55	10.381%	$237.9262	$237.93	$237.95	$237.90
Purchase #3	$126.61	4.168%	$131.8871	$131.89	$131.90	$131.90
Purchase #4	$93.46	7.569%	$100.534	$100.53	$100.55	$100.50
Purchase #5	$50.61	8.140%	$54.7297	$54.73	$54.75	$54.70
Purchase #6	$25.94	3.222%	$26.7758	$26.78	$26.80	$26.80
Purchase #7	$203.63	9.409%	$222.7895	$222.79	$222.80	$222.80
7 purchase totals =	$777.46		$840.4563	$840.46	$840.55	$840.40