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	$38.80	10.516%	$42.8802	$42.88	$42.90	$42.90
Purchase #2	$160.75	3.192%	$165.8811	$165.88	$165.90	$165.90
Purchase #3	$57.78	8.546%	$62.7179	$62.72	$62.70	$62.70
Purchase #4	$91.42	13.653%	$103.9016	$103.90	$103.90	$103.90
Purchase #5	$199.30	13.212%	$225.6315	$225.63	$225.65	$225.60
Purchase #6	$25.41	10.225%	$28.0082	$28.01	$28.00	$28.00
Purchase #7	$244.36	6.472%	$260.175	$260.18	$260.20	$260.20
7 purchase totals =	$817.82		$889.1955	$889.20	$889.25	$889.20