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	$35.39	10.668%	$39.1654	$39.17	$39.15	$39.20
Purchase #2	$121.36	3.759%	$125.9219	$125.92	$125.90	$125.90
Purchase #3	$211.81	12.569%	$238.4324	$238.43	$238.45	$238.40
Purchase #4	$143.56	7.621%	$154.5007	$154.50	$154.50	$154.50
Purchase #5	$138.43	5.544%	$146.1046	$146.10	$146.10	$146.10
Purchase #6	$160.55	9.799%	$176.2823	$176.28	$176.30	$176.30
Purchase #7	$59.39	4.520%	$62.0744	$62.07	$62.05	$62.10
7 purchase totals =	$870.49		$942.4817	$942.47	$942.45	$942.50