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	$63.90	5.779%	$67.5928	$67.59	$67.60	$67.60
Purchase #2	$244.50	11.812%	$273.3803	$273.38	$273.40	$273.40
Purchase #3	$178.59	7.856%	$192.62	$192.62	$192.60	$192.60
Purchase #4	$14.86	5.326%	$15.6514	$15.65	$15.65	$15.70
Purchase #5	$126.51	12.623%	$142.4794	$142.48	$142.50	$142.50
Purchase #6	$52.92	6.182%	$56.1915	$56.19	$56.20	$56.20
Purchase #7	$40.84	4.744%	$42.7774	$42.78	$42.80	$42.80
7 purchase totals =	$722.12		$790.6928	$790.69	$790.75	$790.80