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	$69.86	3.784%	$72.5035	$72.50	$72.50	$72.50
Purchase #2	$182.88	12.114%	$205.0341	$205.03	$205.05	$205.00
Purchase #3	$132.41	6.826%	$141.4483	$141.45	$141.45	$141.40
Purchase #4	$92.28	11.166%	$102.584	$102.58	$102.60	$102.60
Purchase #5	$186.34	11.819%	$208.3635	$208.36	$208.35	$208.40
Purchase #6	$57.52	6.293%	$61.1397	$61.14	$61.15	$61.10
Purchase #7	$63.27	7.408%	$67.957	$67.96	$67.95	$68.00
7 purchase totals =	$784.56		$859.0301	$859.02	$859.05	$859.00