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	$45.93	3.302%	$47.4466	$47.45	$47.45	$47.40
Purchase #2	$209.32	12.669%	$235.8388	$235.84	$235.85	$235.80
Purchase #3	$40.29	5.822%	$42.6357	$42.64	$42.65	$42.60
Purchase #4	$16.78	12.612%	$18.8963	$18.90	$18.90	$18.90
Purchase #5	$68.77	13.441%	$78.0134	$78.01	$78.00	$78.00
Purchase #6	$190.49	12.190%	$213.7107	$213.71	$213.70	$213.70
Purchase #7	$178.82	9.648%	$196.0726	$196.07	$196.05	$196.10
7 purchase totals =	$750.40		$832.6141	$832.62	$832.60	$832.50