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	$12.41	8.790%	$13.5008	$13.50	$13.50	$13.50
Purchase #2	$165.75	13.736%	$188.5174	$188.52	$188.50	$188.50
Purchase #3	$116.81	5.293%	$122.9928	$122.99	$123.00	$123.00
Purchase #4	$110.82	7.469%	$119.0971	$119.10	$119.10	$119.10
Purchase #5	$100.44	11.421%	$111.9113	$111.91	$111.90	$111.90
Purchase #6	$136.99	4.228%	$142.7819	$142.78	$142.80	$142.80
Purchase #7	$42.29	7.500%	$45.4618	$45.46	$45.45	$45.50
7 purchase totals =	$685.51		$744.2631	$744.26	$744.25	$744.30