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	$33.68	8.505%	$36.5445	$36.54	$36.55	$36.50
Purchase #2	$81.32	10.854%	$90.1465	$90.15	$90.15	$90.10
Purchase #3	$132.43	5.197%	$139.3124	$139.31	$139.30	$139.30
Purchase #4	$183.36	5.131%	$192.7682	$192.77	$192.75	$192.80
Purchase #5	$80.83	11.799%	$90.3671	$90.37	$90.35	$90.40
Purchase #6	$164.67	8.573%	$178.7872	$178.79	$178.80	$178.80
Purchase #7	$173.50	6.629%	$185.0013	$185.00	$185.00	$185.00
7 purchase totals =	$849.79		$912.9272	$912.93	$912.90	$912.90