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	$248.27	4.538%	$259.5365	$259.54	$259.55	$259.50
Purchase #2	$150.37	10.630%	$166.3543	$166.35	$166.35	$166.40
Purchase #3	$111.49	4.225%	$116.2005	$116.20	$116.20	$116.20
Purchase #4	$221.60	7.187%	$237.5264	$237.53	$237.55	$237.50
Purchase #5	$52.68	9.448%	$57.6572	$57.66	$57.65	$57.70
Purchase #6	$220.45	10.195%	$242.9249	$242.92	$242.90	$242.90
Purchase #7	$98.56	12.729%	$111.1057	$111.11	$111.10	$111.10
7 purchase totals =	$1,103.42		$1,191.3055	$1,191.31	$1,191.30	$1,191.30