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	$72.57	8.142%	$78.4786	$78.48	$78.50	$78.50
Purchase #2	$23.50	9.696%	$25.7786	$25.78	$25.80	$25.80
Purchase #3	$69.61	11.681%	$77.7411	$77.74	$77.75	$77.70
Purchase #4	$108.37	3.289%	$111.9343	$111.93	$111.95	$111.90
Purchase #5	$41.32	5.767%	$43.7029	$43.70	$43.70	$43.70
Purchase #6	$69.27	8.228%	$74.9695	$74.97	$74.95	$75.00
Purchase #7	$168.96	5.820%	$178.7935	$178.79	$178.80	$178.80
7 purchase totals =	$553.60		$591.3985	$591.39	$591.45	$591.40