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	$175.59	11.791%	$196.2938	$196.29	$196.30	$196.30
Purchase #2	$134.26	11.798%	$150.1	$150.10	$150.10	$150.10
Purchase #3	$52.99	8.688%	$57.5938	$57.59	$57.60	$57.60
Purchase #4	$218.67	13.647%	$248.5119	$248.51	$248.50	$248.50
Purchase #5	$13.92	11.371%	$15.5028	$15.50	$15.50	$15.50
Purchase #6	$94.51	13.449%	$107.2206	$107.22	$107.20	$107.20
Purchase #7	$83.31	6.689%	$88.8826	$88.88	$88.90	$88.90
7 purchase totals =	$773.25		$864.1055	$864.09	$864.10	$864.10