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	$34.45	9.458%	$37.7083	$37.71	$37.70	$37.70
Purchase #2	$10.76	6.424%	$11.4512	$11.45	$11.45	$11.50
Purchase #3	$75.60	6.246%	$80.322	$80.32	$80.30	$80.30
Purchase #4	$67.68	7.563%	$72.7986	$72.80	$72.80	$72.80
Purchase #5	$7.73	11.397%	$8.611	$8.61	$8.60	$8.60
Purchase #6	$23.40	8.347%	$25.3532	$25.35	$25.35	$25.40
Purchase #7	$38.45	10.524%	$42.4965	$42.50	$42.50	$42.50
7 purchase totals =	$258.07		$278.7408	$278.74	$278.70	$278.80