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	$138.69	6.138%	$147.2028	$147.20	$147.20	$147.20
Purchase #2	$156.73	5.212%	$164.8988	$164.90	$164.90	$164.90
Purchase #3	$60.37	7.502%	$64.899	$64.90	$64.90	$64.90
Purchase #4	$153.84	12.161%	$172.5485	$172.55	$172.55	$172.50
Purchase #5	$93.60	7.770%	$100.8727	$100.87	$100.85	$100.90
Purchase #6	$32.86	7.336%	$35.2706	$35.27	$35.25	$35.30
Purchase #7	$32.80	7.248%	$35.1773	$35.18	$35.20	$35.20
7 purchase totals =	$668.89		$720.8697	$720.87	$720.85	$720.90