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	$250.55	8.298%	$271.3406	$271.34	$271.35	$271.30
Purchase #2	$192.33	4.449%	$200.8868	$200.89	$200.90	$200.90
Purchase #3	$164.28	7.673%	$176.8852	$176.89	$176.90	$176.90
Purchase #4	$143.89	4.119%	$149.8168	$149.82	$149.80	$149.80
Purchase #5	$183.92	4.511%	$192.2166	$192.22	$192.20	$192.20
Purchase #6	$122.71	7.153%	$131.4874	$131.49	$131.50	$131.50
Purchase #7	$32.55	10.372%	$35.9261	$35.93	$35.95	$35.90
7 purchase totals =	$1,090.23		$1,158.5595	$1,158.58	$1,158.60	$1,158.50