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	$158.39	12.740%	$178.5689	$178.57	$178.55	$178.60
Purchase #2	$215.52	10.120%	$237.3306	$237.33	$237.35	$237.30
Purchase #3	$40.74	4.325%	$42.502	$42.50	$42.50	$42.50
Purchase #4	$120.48	5.337%	$126.91	$126.91	$126.90	$126.90
Purchase #5	$72.52	11.155%	$80.6096	$80.61	$80.60	$80.60
Purchase #6	$185.45	10.228%	$204.4178	$204.42	$204.40	$204.40
Purchase #7	$95.47	12.712%	$107.6061	$107.61	$107.60	$107.60
7 purchase totals =	$888.57		$977.9450	$977.95	$977.90	$977.90