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	$205.36	12.642%	$231.3216	$231.32	$231.30	$231.30
Purchase #2	$104.66	8.330%	$113.3782	$113.38	$113.40	$113.40
Purchase #3	$161.37	4.324%	$168.3476	$168.35	$168.35	$168.30
Purchase #4	$172.71	13.851%	$196.6321	$196.63	$196.65	$196.60
Purchase #5	$43.72	10.747%	$48.4186	$48.42	$48.40	$48.40
Purchase #6	$68.56	6.193%	$72.8059	$72.81	$72.80	$72.80
Purchase #7	$67.62	3.820%	$70.2031	$70.20	$70.20	$70.20
7 purchase totals =	$824.00		$901.1071	$901.11	$901.10	$901.00