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	$230.66	11.134%	$256.3417	$256.34	$256.35	$256.30
Purchase #2	$142.39	11.328%	$158.5199	$158.52	$158.50	$158.50
Purchase #3	$55.74	11.386%	$62.0866	$62.09	$62.10	$62.10
Purchase #4	$26.27	8.319%	$28.4554	$28.46	$28.45	$28.50
Purchase #5	$37.43	12.817%	$42.2274	$42.23	$42.25	$42.20
Purchase #6	$107.31	8.360%	$116.2811	$116.28	$116.30	$116.30
Purchase #7	$43.56	9.866%	$47.8576	$47.86	$47.85	$47.90
7 purchase totals =	$643.36		$711.7697	$711.78	$711.80	$711.80