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	$38.94	10.402%	$42.9905	$42.99	$43.00	$43.00
Purchase #2	$15.36	3.443%	$15.8888	$15.89	$15.90	$15.90
Purchase #3	$174.67	3.514%	$180.8079	$180.81	$180.80	$180.80
Purchase #4	$67.35	7.856%	$72.641	$72.64	$72.65	$72.60
Purchase #5	$180.63	13.561%	$205.1252	$205.13	$205.15	$205.10
Purchase #6	$185.97	10.711%	$205.8892	$205.89	$205.90	$205.90
Purchase #7	$222.95	6.709%	$237.9077	$237.91	$237.90	$237.90
7 purchase totals =	$885.87		$961.2503	$961.26	$961.30	$961.20