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	$143.82	12.102%	$161.2251	$161.23	$161.25	$161.20
Purchase #2	$144.31	12.857%	$162.8639	$162.86	$162.85	$162.90
Purchase #3	$129.59	10.184%	$142.7874	$142.79	$142.80	$142.80
Purchase #4	$38.40	12.807%	$43.3179	$43.32	$43.30	$43.30
Purchase #5	$76.46	11.803%	$85.4846	$85.48	$85.50	$85.50
Purchase #6	$142.80	10.184%	$157.3428	$157.34	$157.35	$157.30
Purchase #7	$43.77	7.543%	$47.0716	$47.07	$47.05	$47.10
7 purchase totals =	$719.15		$800.0933	$800.09	$800.10	$800.10