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	$137.39	3.522%	$142.2289	$142.23	$142.25	$142.20
Purchase #2	$158.65	11.462%	$176.8345	$176.83	$176.85	$176.80
Purchase #3	$77.87	10.563%	$86.0954	$86.10	$86.10	$86.10
Purchase #4	$65.90	12.112%	$73.8818	$73.88	$73.90	$73.90
Purchase #5	$115.42	3.659%	$119.6432	$119.64	$119.65	$119.60
Purchase #6	$245.96	10.419%	$271.5866	$271.59	$271.60	$271.60
Purchase #7	$126.60	8.576%	$137.4572	$137.46	$137.45	$137.50
7 purchase totals =	$927.79		$1,007.7276	$1,007.73	$1,007.80	$1,007.70