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	$74.56	5.352%	$78.5505	$78.55	$78.55	$78.60
Purchase #2	$100.59	8.666%	$109.3071	$109.31	$109.30	$109.30
Purchase #3	$233.47	12.252%	$262.0747	$262.07	$262.05	$262.10
Purchase #4	$178.99	3.664%	$185.5482	$185.55	$185.55	$185.50
Purchase #5	$85.82	10.246%	$94.6131	$94.61	$94.60	$94.60
Purchase #6	$243.47	8.639%	$264.5034	$264.50	$264.50	$264.50
Purchase #7	$237.92	11.640%	$265.6139	$265.61	$265.60	$265.60
7 purchase totals =	$1,154.82		$1,260.2109	$1,260.20	$1,260.15	$1,260.20