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	$42.86	10.868%	$47.518	$47.52	$47.50	$47.50
Purchase #2	$39.89	6.663%	$42.5479	$42.55	$42.55	$42.50
Purchase #3	$124.32	12.247%	$139.5455	$139.55	$139.55	$139.50
Purchase #4	$191.54	5.713%	$202.4827	$202.48	$202.50	$202.50
Purchase #5	$103.66	13.116%	$117.256	$117.26	$117.25	$117.30
Purchase #6	$134.77	7.229%	$144.5125	$144.51	$144.50	$144.50
Purchase #7	$180.80	12.578%	$203.541	$203.54	$203.55	$203.50
7 purchase totals =	$817.84		$897.4036	$897.41	$897.40	$897.30