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	$125.25	10.417%	$138.2973	$138.30	$138.30	$138.30
Purchase #2	$237.42	12.409%	$266.8814	$266.88	$266.90	$266.90
Purchase #3	$29.48	13.578%	$33.4828	$33.48	$33.50	$33.50
Purchase #4	$10.72	12.160%	$12.0236	$12.02	$12.00	$12.00
Purchase #5	$232.76	12.136%	$261.0078	$261.01	$261.00	$261.00
Purchase #6	$80.54	6.288%	$85.6044	$85.60	$85.60	$85.60
Purchase #7	$140.27	13.260%	$158.8698	$158.87	$158.85	$158.90
7 purchase totals =	$856.44		$956.1671	$956.16	$956.15	$956.20