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	$73.63	6.499%	$78.4152	$78.42	$78.40	$78.40
Purchase #2	$221.94	13.730%	$252.4124	$252.41	$252.40	$252.40
Purchase #3	$158.89	13.483%	$180.3131	$180.31	$180.30	$180.30
Purchase #4	$119.39	3.238%	$123.2558	$123.26	$123.25	$123.30
Purchase #5	$83.50	12.384%	$93.8406	$93.84	$93.85	$93.80
Purchase #6	$228.89	5.437%	$241.3347	$241.33	$241.35	$241.30
Purchase #7	$105.38	12.308%	$118.3502	$118.35	$118.35	$118.40
7 purchase totals =	$991.62		$1,087.9220	$1,087.92	$1,087.90	$1,087.90