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	$236.42	10.669%	$261.6436	$261.64	$261.65	$261.60
Purchase #2	$78.40	8.799%	$85.2984	$85.30	$85.30	$85.30
Purchase #3	$241.84	9.817%	$265.5814	$265.58	$265.60	$265.60
Purchase #4	$173.50	6.325%	$184.4739	$184.47	$184.45	$184.50
Purchase #5	$13.95	11.621%	$15.5711	$15.57	$15.55	$15.60
Purchase #6	$55.76	3.766%	$57.8599	$57.86	$57.85	$57.90
Purchase #7	$134.25	9.330%	$146.7755	$146.78	$146.80	$146.80
7 purchase totals =	$934.12		$1,017.2038	$1,017.20	$1,017.20	$1,017.30