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	$84.93	9.408%	$92.9202	$92.92	$92.90	$92.90
Purchase #2	$80.91	10.788%	$89.6386	$89.64	$89.65	$89.60
Purchase #3	$112.96	8.454%	$122.5096	$122.51	$122.50	$122.50
Purchase #4	$164.41	3.777%	$170.6198	$170.62	$170.60	$170.60
Purchase #5	$147.31	13.716%	$167.515	$167.52	$167.50	$167.50
Purchase #6	$115.60	6.483%	$123.0943	$123.09	$123.10	$123.10
Purchase #7	$90.89	6.584%	$96.8742	$96.87	$96.85	$96.90
7 purchase totals =	$797.01		$863.1717	$863.17	$863.10	$863.10