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	$38.57	6.162%	$40.9467	$40.95	$40.95	$40.90
Purchase #2	$147.41	11.725%	$164.6938	$164.69	$164.70	$164.70
Purchase #3	$42.43	12.310%	$47.6531	$47.65	$47.65	$47.70
Purchase #4	$55.50	11.375%	$61.8131	$61.81	$61.80	$61.80
Purchase #5	$55.46	9.613%	$60.7914	$60.79	$60.80	$60.80
Purchase #6	$87.71	8.632%	$95.2811	$95.28	$95.30	$95.30
Purchase #7	$100.97	11.606%	$112.6886	$112.69	$112.70	$112.70
7 purchase totals =	$528.05		$583.8678	$583.86	$583.90	$583.90