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	$49.81	11.264%	$55.4206	$55.42	$55.40	$55.40
Purchase #2	$209.88	10.765%	$232.4736	$232.47	$232.45	$232.50
Purchase #3	$228.80	10.820%	$253.5562	$253.56	$253.55	$253.60
Purchase #4	$192.69	4.250%	$200.8793	$200.88	$200.90	$200.90
Purchase #5	$83.49	7.834%	$90.0306	$90.03	$90.05	$90.00
Purchase #6	$105.52	3.569%	$109.286	$109.29	$109.30	$109.30
Purchase #7	$129.68	3.823%	$134.6377	$134.64	$134.65	$134.60
7 purchase totals =	$999.87		$1,076.2840	$1,076.29	$1,076.30	$1,076.30