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	$80.28	12.760%	$90.5237	$90.52	$90.50	$90.50
Purchase #2	$22.89	4.837%	$23.9972	$24.00	$24.00	$24.00
Purchase #3	$37.90	12.412%	$42.6041	$42.60	$42.60	$42.60
Purchase #4	$91.58	7.863%	$98.7809	$98.78	$98.80	$98.80
Purchase #5	$167.33	4.735%	$175.2531	$175.25	$175.25	$175.30
Purchase #6	$216.86	9.397%	$237.2383	$237.24	$237.25	$237.20
Purchase #7	$65.70	7.375%	$70.5454	$70.55	$70.55	$70.50
7 purchase totals =	$682.54		$738.9427	$738.94	$738.95	$738.90