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	$72.59	8.790%	$78.9707	$78.97	$78.95	$79.00
Purchase #2	$161.88	4.218%	$168.7081	$168.71	$168.70	$168.70
Purchase #3	$127.39	13.692%	$144.8322	$144.83	$144.85	$144.80
Purchase #4	$95.25	12.372%	$107.0343	$107.03	$107.05	$107.00
Purchase #5	$213.58	3.222%	$220.4615	$220.46	$220.45	$220.50
Purchase #6	$146.69	3.490%	$151.8095	$151.81	$151.80	$151.80
Purchase #7	$56.76	9.532%	$62.1704	$62.17	$62.15	$62.20
7 purchase totals =	$874.14		$933.9867	$933.98	$933.95	$934.00