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	$19.44	3.808%	$20.1803	$20.18	$20.20	$20.20
Purchase #2	$48.74	4.463%	$50.9153	$50.92	$50.90	$50.90
Purchase #3	$51.79	4.164%	$53.9465	$53.95	$53.95	$53.90
Purchase #4	$7.46	4.468%	$7.7933	$7.79	$7.80	$7.80
Purchase #5	$134.29	6.185%	$142.5958	$142.60	$142.60	$142.60
Purchase #6	$239.27	9.715%	$262.5151	$262.52	$262.50	$262.50
Purchase #7	$242.79	10.341%	$267.8969	$267.90	$267.90	$267.90
7 purchase totals =	$743.78		$805.8432	$805.86	$805.85	$805.80