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	$105.52	6.726%	$112.6173	$112.62	$112.60	$112.60
Purchase #2	$81.89	13.435%	$92.8919	$92.89	$92.90	$92.90
Purchase #3	$206.56	4.787%	$216.448	$216.45	$216.45	$216.40
Purchase #4	$112.88	7.494%	$121.3392	$121.34	$121.35	$121.30
Purchase #5	$104.47	4.342%	$109.0061	$109.01	$109.00	$109.00
Purchase #6	$183.59	3.193%	$189.452	$189.45	$189.45	$189.50
Purchase #7	$43.52	9.449%	$47.6322	$47.63	$47.65	$47.60
7 purchase totals =	$838.43		$889.3867	$889.39	$889.40	$889.30