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	$134.37	13.575%	$152.6107	$152.61	$152.60	$152.60
Purchase #2	$139.73	8.829%	$152.0668	$152.07	$152.05	$152.10
Purchase #3	$177.73	10.541%	$196.4645	$196.46	$196.45	$196.50
Purchase #4	$43.65	4.323%	$45.537	$45.54	$45.55	$45.50
Purchase #5	$51.93	6.373%	$55.2395	$55.24	$55.25	$55.20
Purchase #6	$27.78	12.604%	$31.2814	$31.28	$31.30	$31.30
Purchase #7	$31.54	5.559%	$33.2933	$33.29	$33.30	$33.30
7 purchase totals =	$606.73		$666.4932	$666.49	$666.50	$666.50