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	$130.38	4.788%	$136.6226	$136.62	$136.60	$136.60
Purchase #2	$222.51	8.551%	$241.5368	$241.54	$241.55	$241.50
Purchase #3	$164.99	10.379%	$182.1143	$182.11	$182.10	$182.10
Purchase #4	$134.66	12.468%	$151.4494	$151.45	$151.45	$151.40
Purchase #5	$173.80	9.801%	$190.8341	$190.83	$190.85	$190.80
Purchase #6	$27.86	5.279%	$29.3307	$29.33	$29.35	$29.30
Purchase #7	$102.58	7.384%	$110.1545	$110.15	$110.15	$110.20
7 purchase totals =	$956.78		$1,042.0424	$1,042.03	$1,042.05	$1,041.90