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	$240.86	3.587%	$249.4996	$249.50	$249.50	$249.50
Purchase #2	$33.40	5.198%	$35.1361	$35.14	$35.15	$35.10
Purchase #3	$161.58	4.546%	$168.9254	$168.93	$168.95	$168.90
Purchase #4	$131.41	7.338%	$141.0529	$141.05	$141.05	$141.10
Purchase #5	$35.25	5.162%	$37.0696	$37.07	$37.05	$37.10
Purchase #6	$35.75	4.637%	$37.4077	$37.41	$37.40	$37.40
Purchase #7	$61.27	12.780%	$69.1003	$69.10	$69.10	$69.10
7 purchase totals =	$699.52		$738.1916	$738.20	$738.20	$738.20