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	$59.63	4.759%	$62.4678	$62.47	$62.45	$62.50
Purchase #2	$159.25	6.302%	$169.2859	$169.29	$169.30	$169.30
Purchase #3	$78.50	5.402%	$82.7406	$82.74	$82.75	$82.70
Purchase #4	$30.99	3.447%	$32.0582	$32.06	$32.05	$32.10
Purchase #5	$124.26	6.582%	$132.4388	$132.44	$132.45	$132.40
Purchase #6	$6.33	4.170%	$6.594	$6.59	$6.60	$6.60
Purchase #7	$135.59	13.767%	$154.2567	$154.26	$154.25	$154.30
7 purchase totals =	$594.55		$639.8420	$639.85	$639.85	$639.90