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	$133.42	9.348%	$145.8921	$145.89	$145.90	$145.90
Purchase #2	$130.81	5.484%	$137.9836	$137.98	$138.00	$138.00
Purchase #3	$235.56	3.416%	$243.6067	$243.61	$243.60	$243.60
Purchase #4	$68.29	3.342%	$70.5723	$70.57	$70.55	$70.60
Purchase #5	$238.70	8.606%	$259.2425	$259.24	$259.25	$259.20
Purchase #6	$11.55	4.788%	$12.103	$12.10	$12.10	$12.10
Purchase #7	$126.41	6.368%	$134.4598	$134.46	$134.45	$134.50
7 purchase totals =	$944.74		$1,003.8600	$1,003.85	$1,003.85	$1,003.90