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	$201.29	9.405%	$220.2213	$220.22	$220.20	$220.20
Purchase #2	$170.84	12.357%	$191.9507	$191.95	$191.95	$192.00
Purchase #3	$119.30	9.583%	$130.7325	$130.73	$130.75	$130.70
Purchase #4	$107.48	4.103%	$111.8899	$111.89	$111.90	$111.90
Purchase #5	$119.46	7.358%	$128.2499	$128.25	$128.25	$128.20
Purchase #6	$35.29	10.276%	$38.9164	$38.92	$38.90	$38.90
Purchase #7	$102.47	9.270%	$111.969	$111.97	$111.95	$112.00
7 purchase totals =	$856.13		$933.9297	$933.93	$933.90	$933.90