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	$225.77	5.418%	$238.0022	$238.00	$238.00	$238.00
Purchase #2	$237.86	7.376%	$255.4046	$255.40	$255.40	$255.40
Purchase #3	$69.53	12.648%	$78.3242	$78.32	$78.30	$78.30
Purchase #4	$43.63	4.142%	$45.4372	$45.44	$45.45	$45.40
Purchase #5	$16.35	12.301%	$18.3612	$18.36	$18.35	$18.40
Purchase #6	$177.49	11.665%	$198.1942	$198.19	$198.20	$198.20
Purchase #7	$11.42	3.144%	$11.779	$11.78	$11.80	$11.80
7 purchase totals =	$782.05		$845.5026	$845.49	$845.50	$845.50