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	$81.61	10.425%	$90.1178	$90.12	$90.10	$90.10
Purchase #2	$138.67	6.636%	$147.8721	$147.87	$147.85	$147.90
Purchase #3	$124.67	6.508%	$132.7835	$132.78	$132.80	$132.80
Purchase #4	$74.48	5.328%	$78.4483	$78.45	$78.45	$78.40
Purchase #5	$87.49	9.525%	$95.8234	$95.82	$95.80	$95.80
Purchase #6	$38.95	3.847%	$40.4484	$40.45	$40.45	$40.40
Purchase #7	$12.70	9.524%	$13.9095	$13.91	$13.90	$13.90
7 purchase totals =	$558.57		$599.4030	$599.40	$599.35	$599.30