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	$93.67	6.262%	$99.5356	$99.54	$99.55	$99.50
Purchase #2	$38.69	5.666%	$40.8822	$40.88	$40.90	$40.90
Purchase #3	$85.36	9.582%	$93.5392	$93.54	$93.55	$93.50
Purchase #4	$183.78	8.233%	$198.9106	$198.91	$198.90	$198.90
Purchase #5	$9.25	9.586%	$10.1367	$10.14	$10.15	$10.10
Purchase #6	$119.54	3.681%	$123.9403	$123.94	$123.95	$123.90
Purchase #7	$233.66	11.497%	$260.5239	$260.52	$260.50	$260.50
7 purchase totals =	$763.95		$827.4685	$827.47	$827.50	$827.30