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	$38.79	3.676%	$40.2159	$40.22	$40.20	$40.20
Purchase #2	$10.59	9.809%	$11.6288	$11.63	$11.65	$11.60
Purchase #3	$139.37	11.293%	$155.1091	$155.11	$155.10	$155.10
Purchase #4	$87.82	12.774%	$99.0381	$99.04	$99.05	$99.00
Purchase #5	$249.40	9.242%	$272.4495	$272.45	$272.45	$272.40
Purchase #6	$220.78	11.527%	$246.2293	$246.23	$246.25	$246.20
Purchase #7	$217.88	13.262%	$246.7752	$246.78	$246.80	$246.80
7 purchase totals =	$964.63		$1,071.4459	$1,071.46	$1,071.50	$1,071.30