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	$239.85	6.406%	$255.2148	$255.21	$255.20	$255.20
Purchase #2	$211.54	11.845%	$236.5969	$236.60	$236.60	$236.60
Purchase #3	$80.56	11.278%	$89.6456	$89.65	$89.65	$89.60
Purchase #4	$129.47	6.229%	$137.5347	$137.53	$137.55	$137.50
Purchase #5	$6.98	3.697%	$7.2381	$7.24	$7.25	$7.20
Purchase #6	$237.81	7.840%	$256.4543	$256.45	$256.45	$256.50
Purchase #7	$126.40	12.768%	$142.5388	$142.54	$142.55	$142.50
7 purchase totals =	$1,032.61		$1,125.2232	$1,125.22	$1,125.25	$1,125.10