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	$15.79	11.196%	$17.5578	$17.56	$17.55	$17.60
Purchase #2	$69.56	11.279%	$77.4057	$77.41	$77.40	$77.40
Purchase #3	$141.29	6.469%	$150.4301	$150.43	$150.45	$150.40
Purchase #4	$205.56	4.711%	$215.2439	$215.24	$215.25	$215.20
Purchase #5	$98.57	4.669%	$103.1722	$103.17	$103.15	$103.20
Purchase #6	$40.58	13.801%	$46.1804	$46.18	$46.20	$46.20
Purchase #7	$119.36	9.652%	$130.8806	$130.88	$130.90	$130.90
7 purchase totals =	$690.71		$740.8707	$740.87	$740.90	$740.90