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	$157.89	6.282%	$167.8086	$167.81	$167.80	$167.80
Purchase #2	$66.78	5.599%	$70.519	$70.52	$70.50	$70.50
Purchase #3	$37.60	12.209%	$42.1906	$42.19	$42.20	$42.20
Purchase #4	$150.38	11.617%	$167.8496	$167.85	$167.85	$167.80
Purchase #5	$147.38	6.836%	$157.4549	$157.45	$157.45	$157.50
Purchase #6	$108.63	5.163%	$114.2386	$114.24	$114.25	$114.20
Purchase #7	$105.96	12.618%	$119.33	$119.33	$119.35	$119.30
7 purchase totals =	$774.62		$839.3913	$839.39	$839.40	$839.30