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	$7.58	8.382%	$8.2154	$8.22	$8.20	$8.20
Purchase #2	$71.50	3.187%	$73.7787	$73.78	$73.80	$73.80
Purchase #3	$148.50	10.716%	$164.4133	$164.41	$164.40	$164.40
Purchase #4	$123.40	5.422%	$130.0907	$130.09	$130.10	$130.10
Purchase #5	$78.27	7.147%	$83.864	$83.86	$83.85	$83.90
Purchase #6	$192.81	3.151%	$198.8854	$198.89	$198.90	$198.90
Purchase #7	$35.75	11.558%	$39.882	$39.88	$39.90	$39.90
7 purchase totals =	$657.81		$699.1295	$699.13	$699.15	$699.20