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	$72.33	8.382%	$78.3927	$78.39	$78.40	$78.40
Purchase #2	$135.70	6.458%	$144.4635	$144.46	$144.45	$144.50
Purchase #3	$83.76	4.518%	$87.5443	$87.54	$87.55	$87.50
Purchase #4	$246.60	12.858%	$278.3078	$278.31	$278.30	$278.30
Purchase #5	$30.30	7.322%	$32.5186	$32.52	$32.50	$32.50
Purchase #6	$220.76	4.872%	$231.5154	$231.52	$231.50	$231.50
Purchase #7	$206.46	3.543%	$213.7749	$213.77	$213.75	$213.80
7 purchase totals =	$995.91		$1,066.5172	$1,066.51	$1,066.45	$1,066.50