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	$243.66	10.723%	$269.7877	$269.79	$269.80	$269.80
Purchase #2	$187.78	10.180%	$206.896	$206.90	$206.90	$206.90
Purchase #3	$15.94	13.351%	$18.0681	$18.07	$18.05	$18.10
Purchase #4	$73.35	9.763%	$80.5112	$80.51	$80.50	$80.50
Purchase #5	$18.76	8.568%	$20.3674	$20.37	$20.35	$20.40
Purchase #6	$142.89	5.644%	$150.9547	$150.95	$150.95	$151.00
Purchase #7	$52.92	3.165%	$54.5949	$54.59	$54.60	$54.60
7 purchase totals =	$735.30		$801.1800	$801.18	$801.15	$801.30