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	$9.44	12.343%	$10.6052	$10.61	$10.60	$10.60
Purchase #2	$215.34	3.437%	$222.7412	$222.74	$222.75	$222.70
Purchase #3	$145.51	9.589%	$159.463	$159.46	$159.45	$159.50
Purchase #4	$113.63	9.841%	$124.8123	$124.81	$124.80	$124.80
Purchase #5	$72.39	10.861%	$80.2523	$80.25	$80.25	$80.30
Purchase #6	$38.79	7.749%	$41.7958	$41.80	$41.80	$41.80
Purchase #7	$122.94	6.745%	$131.2323	$131.23	$131.25	$131.20
7 purchase totals =	$718.04		$770.9021	$770.90	$770.90	$770.90