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	$56.50	3.238%	$58.3295	$58.33	$58.35	$58.30
Purchase #2	$17.51	3.321%	$18.0915	$18.09	$18.10	$18.10
Purchase #3	$137.57	11.585%	$153.5075	$153.51	$153.50	$153.50
Purchase #4	$30.98	5.479%	$32.6774	$32.68	$32.70	$32.70
Purchase #5	$152.89	7.851%	$164.8934	$164.89	$164.90	$164.90
Purchase #6	$181.82	9.597%	$199.2693	$199.27	$199.25	$199.30
Purchase #7	$116.63	13.561%	$132.4462	$132.45	$132.45	$132.40
7 purchase totals =	$693.90		$759.2148	$759.22	$759.25	$759.20