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	$197.44	6.302%	$209.8827	$209.88	$209.90	$209.90
Purchase #2	$81.57	8.868%	$88.8036	$88.80	$88.80	$88.80
Purchase #3	$143.57	10.422%	$158.5329	$158.53	$158.55	$158.50
Purchase #4	$105.60	4.724%	$110.5885	$110.59	$110.60	$110.60
Purchase #5	$80.58	11.376%	$89.7468	$89.75	$89.75	$89.70
Purchase #6	$69.72	4.722%	$73.0122	$73.01	$73.00	$73.00
Purchase #7	$75.69	3.837%	$78.5942	$78.59	$78.60	$78.60
7 purchase totals =	$754.17		$809.1609	$809.15	$809.20	$809.10