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	$18.74	6.839%	$20.0216	$20.02	$20.00	$20.00
Purchase #2	$103.70	7.166%	$111.1311	$111.13	$111.15	$111.10
Purchase #3	$67.93	8.209%	$73.5064	$73.51	$73.50	$73.50
Purchase #4	$79.62	5.445%	$83.9553	$83.96	$83.95	$84.00
Purchase #5	$128.95	10.567%	$142.5761	$142.58	$142.60	$142.60
Purchase #6	$200.55	3.462%	$207.493	$207.49	$207.50	$207.50
Purchase #7	$136.39	4.341%	$142.3107	$142.31	$142.30	$142.30
7 purchase totals =	$735.88		$780.9942	$781.00	$781.00	$781.00