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	$34.39	8.381%	$37.2722	$37.27	$37.25	$37.30
Purchase #2	$171.82	4.810%	$180.0845	$180.08	$180.10	$180.10
Purchase #3	$85.35	5.526%	$90.0664	$90.07	$90.05	$90.10
Purchase #4	$51.55	7.408%	$55.3688	$55.37	$55.35	$55.40
Purchase #5	$27.81	11.775%	$31.0846	$31.08	$31.10	$31.10
Purchase #6	$19.93	10.622%	$22.047	$22.05	$22.05	$22.00
Purchase #7	$141.76	8.589%	$153.9358	$153.94	$153.95	$153.90
7 purchase totals =	$532.61		$569.8593	$569.86	$569.85	$569.90