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	$68.93	13.611%	$78.3121	$78.31	$78.30	$78.30
Purchase #2	$98.76	12.451%	$111.0566	$111.06	$111.05	$111.10
Purchase #3	$121.49	3.663%	$125.9402	$125.94	$125.95	$125.90
Purchase #4	$196.66	11.151%	$218.5896	$218.59	$218.60	$218.60
Purchase #5	$233.56	13.462%	$265.0018	$265.00	$265.00	$265.00
Purchase #6	$42.92	5.301%	$45.1952	$45.20	$45.20	$45.20
Purchase #7	$6.50	12.868%	$7.3364	$7.34	$7.35	$7.30
7 purchase totals =	$768.82		$851.4319	$851.44	$851.45	$851.40