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	$15.83	5.264%	$16.6633	$16.66	$16.65	$16.70
Purchase #2	$248.97	9.850%	$273.4935	$273.49	$273.50	$273.50
Purchase #3	$241.84	9.777%	$265.4847	$265.48	$265.50	$265.50
Purchase #4	$70.32	3.108%	$72.5055	$72.51	$72.50	$72.50
Purchase #5	$118.54	8.656%	$128.8008	$128.80	$128.80	$128.80
Purchase #6	$87.34	3.282%	$90.2065	$90.21	$90.20	$90.20
Purchase #7	$247.66	4.277%	$258.2524	$258.25	$258.25	$258.30
7 purchase totals =	$1,030.50		$1,105.4067	$1,105.40	$1,105.40	$1,105.50