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	$123.76	6.465%	$131.7611	$131.76	$131.75	$131.80
Purchase #2	$103.44	7.595%	$111.2963	$111.30	$111.30	$111.30
Purchase #3	$111.36	4.590%	$116.4714	$116.47	$116.45	$116.50
Purchase #4	$126.88	13.542%	$144.0621	$144.06	$144.05	$144.10
Purchase #5	$55.99	3.722%	$58.0739	$58.07	$58.05	$58.10
Purchase #6	$137.99	13.151%	$156.1371	$156.14	$156.15	$156.10
Purchase #7	$44.70	13.736%	$50.84	$50.84	$50.85	$50.80
7 purchase totals =	$704.12		$768.6419	$768.64	$768.60	$768.70