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	$137.34	4.216%	$143.1303	$143.13	$143.15	$143.10
Purchase #2	$154.54	6.411%	$164.4476	$164.45	$164.45	$164.40
Purchase #3	$8.84	7.389%	$9.4932	$9.49	$9.50	$9.50
Purchase #4	$207.49	11.484%	$231.3182	$231.32	$231.30	$231.30
Purchase #5	$139.96	5.208%	$147.2491	$147.25	$147.25	$147.20
Purchase #6	$78.58	13.812%	$89.4335	$89.43	$89.45	$89.40
Purchase #7	$87.84	5.271%	$92.47	$92.47	$92.45	$92.50
7 purchase totals =	$814.59		$877.5419	$877.54	$877.55	$877.40