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	$39.78	6.874%	$42.5145	$42.51	$42.50	$42.50
Purchase #2	$246.88	3.371%	$255.2023	$255.20	$255.20	$255.20
Purchase #3	$202.57	9.716%	$222.2517	$222.25	$222.25	$222.30
Purchase #4	$154.87	4.664%	$162.0931	$162.09	$162.10	$162.10
Purchase #5	$19.76	11.573%	$22.0468	$22.05	$22.05	$22.00
Purchase #6	$236.63	10.105%	$260.5415	$260.54	$260.55	$260.50
Purchase #7	$64.67	12.359%	$72.6626	$72.66	$72.65	$72.70
7 purchase totals =	$965.16		$1,037.3125	$1,037.30	$1,037.30	$1,037.30