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	$161.85	13.284%	$183.3502	$183.35	$183.35	$183.40
Purchase #2	$90.99	9.146%	$99.3119	$99.31	$99.30	$99.30
Purchase #3	$242.62	7.536%	$260.9038	$260.90	$260.90	$260.90
Purchase #4	$198.64	7.384%	$213.3076	$213.31	$213.30	$213.30
Purchase #5	$85.97	5.143%	$90.3914	$90.39	$90.40	$90.40
Purchase #6	$36.35	11.735%	$40.6157	$40.62	$40.60	$40.60
Purchase #7	$67.67	7.269%	$72.5889	$72.59	$72.60	$72.60
7 purchase totals =	$884.09		$960.4695	$960.47	$960.45	$960.50