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	$19.80	12.661%	$22.3069	$22.31	$22.30	$22.30
Purchase #2	$86.44	10.447%	$95.4704	$95.47	$95.45	$95.50
Purchase #3	$212.82	12.236%	$238.8607	$238.86	$238.85	$238.90
Purchase #4	$30.52	13.302%	$34.5798	$34.58	$34.60	$34.60
Purchase #5	$103.82	10.331%	$114.5456	$114.55	$114.55	$114.50
Purchase #6	$64.79	13.250%	$73.3747	$73.37	$73.35	$73.40
Purchase #7	$149.71	7.383%	$160.7631	$160.76	$160.75	$160.80
7 purchase totals =	$667.90		$739.9012	$739.90	$739.85	$740.00