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	$32.99	7.855%	$35.5814	$35.58	$35.60	$35.60
Purchase #2	$244.88	12.504%	$275.4998	$275.50	$275.50	$275.50
Purchase #3	$144.92	4.105%	$150.869	$150.87	$150.85	$150.90
Purchase #4	$50.44	7.720%	$54.334	$54.33	$54.35	$54.30
Purchase #5	$110.42	8.547%	$119.8576	$119.86	$119.85	$119.90
Purchase #6	$132.61	6.310%	$140.9777	$140.98	$141.00	$141.00
Purchase #7	$121.80	4.680%	$127.5002	$127.50	$127.50	$127.50
7 purchase totals =	$838.06		$904.6197	$904.62	$904.65	$904.70