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	$6.88	13.226%	$7.7899	$7.79	$7.80	$7.80
Purchase #2	$41.55	4.317%	$43.3437	$43.34	$43.35	$43.30
Purchase #3	$157.49	10.191%	$173.5398	$173.54	$173.55	$173.50
Purchase #4	$209.39	5.358%	$220.6091	$220.61	$220.60	$220.60
Purchase #5	$190.77	13.378%	$216.2912	$216.29	$216.30	$216.30
Purchase #6	$126.42	3.704%	$131.1026	$131.10	$131.10	$131.10
Purchase #7	$97.50	12.176%	$109.3716	$109.37	$109.35	$109.40
7 purchase totals =	$830.00		$902.0479	$902.04	$902.05	$902.00