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	$51.57	6.292%	$54.8148	$54.81	$54.80	$54.80
Purchase #2	$139.29	11.867%	$155.8195	$155.82	$155.80	$155.80
Purchase #3	$56.65	7.661%	$60.99	$60.99	$61.00	$61.00
Purchase #4	$226.42	10.682%	$250.6062	$250.61	$250.60	$250.60
Purchase #5	$86.87	6.726%	$92.7129	$92.71	$92.70	$92.70
Purchase #6	$238.92	6.793%	$255.1498	$255.15	$255.15	$255.10
Purchase #7	$56.84	10.727%	$62.9372	$62.94	$62.95	$62.90
7 purchase totals =	$856.56		$933.0304	$933.03	$933.00	$932.90