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	$91.64	3.438%	$94.7906	$94.79	$94.80	$94.80
Purchase #2	$219.93	9.857%	$241.6085	$241.61	$241.60	$241.60
Purchase #3	$42.76	6.700%	$45.6249	$45.62	$45.60	$45.60
Purchase #4	$250.51	11.641%	$279.6719	$279.67	$279.65	$279.70
Purchase #5	$234.45	9.205%	$256.0311	$256.03	$256.05	$256.00
Purchase #6	$160.42	6.253%	$170.4511	$170.45	$170.45	$170.50
Purchase #7	$222.46	12.600%	$250.49	$250.49	$250.50	$250.50
7 purchase totals =	$1,222.17		$1,338.6681	$1,338.66	$1,338.65	$1,338.70