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	$100.35	8.261%	$108.6399	$108.64	$108.65	$108.60
Purchase #2	$69.60	13.332%	$78.8791	$78.88	$78.90	$78.90
Purchase #3	$132.54	11.228%	$147.4216	$147.42	$147.40	$147.40
Purchase #4	$87.60	13.566%	$99.4838	$99.48	$99.50	$99.50
Purchase #5	$137.37	13.660%	$156.1347	$156.13	$156.15	$156.10
Purchase #6	$226.76	12.241%	$254.5177	$254.52	$254.50	$254.50
Purchase #7	$73.98	3.466%	$76.5441	$76.54	$76.55	$76.50
7 purchase totals =	$828.20		$921.6209	$921.61	$921.65	$921.50