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	$74.72	7.329%	$80.1962	$80.20	$80.20	$80.20
Purchase #2	$116.45	11.544%	$129.893	$129.89	$129.90	$129.90
Purchase #3	$242.76	6.376%	$258.2384	$258.24	$258.25	$258.20
Purchase #4	$199.85	4.382%	$208.6074	$208.61	$208.60	$208.60
Purchase #5	$38.89	10.428%	$42.9454	$42.95	$42.95	$42.90
Purchase #6	$208.93	5.583%	$220.5946	$220.59	$220.60	$220.60
Purchase #7	$72.83	11.761%	$81.3955	$81.40	$81.40	$81.40
7 purchase totals =	$954.43		$1,021.8705	$1,021.88	$1,021.90	$1,021.80