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	$245.59	7.660%	$264.4022	$264.40	$264.40	$264.40
Purchase #2	$101.90	3.766%	$105.7376	$105.74	$105.75	$105.70
Purchase #3	$136.49	13.861%	$155.4089	$155.41	$155.40	$155.40
Purchase #4	$73.34	7.490%	$78.8332	$78.83	$78.85	$78.80
Purchase #5	$114.74	12.460%	$129.0366	$129.04	$129.05	$129.00
Purchase #6	$150.65	9.451%	$164.8879	$164.89	$164.90	$164.90
Purchase #7	$6.83	4.365%	$7.1281	$7.13	$7.15	$7.10
7 purchase totals =	$829.54		$905.4345	$905.44	$905.50	$905.30