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	$46.89	10.597%	$51.8589	$51.86	$51.85	$51.90
Purchase #2	$139.42	4.255%	$145.3523	$145.35	$145.35	$145.40
Purchase #3	$44.70	12.385%	$50.2361	$50.24	$50.25	$50.20
Purchase #4	$180.29	4.204%	$187.8694	$187.87	$187.85	$187.90
Purchase #5	$54.77	8.533%	$59.4435	$59.44	$59.45	$59.40
Purchase #6	$196.40	12.825%	$221.5883	$221.59	$221.60	$221.60
Purchase #7	$203.32	13.661%	$231.0955	$231.10	$231.10	$231.10
7 purchase totals =	$865.79		$947.4440	$947.45	$947.45	$947.50