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	$238.86	13.171%	$270.3203	$270.32	$270.30	$270.30
Purchase #2	$164.35	6.706%	$175.3713	$175.37	$175.35	$175.40
Purchase #3	$126.64	9.204%	$138.2959	$138.30	$138.30	$138.30
Purchase #4	$118.26	11.213%	$131.5205	$131.52	$131.50	$131.50
Purchase #5	$98.25	5.247%	$103.4052	$103.41	$103.40	$103.40
Purchase #6	$245.25	4.557%	$256.426	$256.43	$256.45	$256.40
Purchase #7	$237.28	6.722%	$253.23	$253.23	$253.25	$253.20
7 purchase totals =	$1,228.89		$1,328.5692	$1,328.58	$1,328.55	$1,328.50